[a / b / c / d / e / f / g / gif / h / hr / k / m / o / p / r / s / t / u / v / vg / vm / vmg / vr / vrpg / vst / w / wg] [i / ic] [r9k / s4s / vip / qa] [cm / hm / lgbt / y] [3 / aco / adv / an / asp / bant / biz / cgl / ck / co / diy / fa / fit / gd / hc / his / int / jp / lit / mlp / mu / n / news / out / po / pol / qst / sci / soc / sp / tg / toy / trv / tv / vp / wsg / wsr / x] [Settings] [Search] [Mobile] [Home]
Board
Settings Mobile Home
/sci/ - Science & Math

[Advertise on 4chan]


Thread archived.
You cannot reply anymore.


[Advertise on 4chan]


File: 1605488732586.jpg (72 KB, 736x981)
72 KB
72 KB JPG
Previously >>12332227

>what is /sqt/ for
Questions regarding math and science, plus related advice requests.
>where do I go for other SFW questions and (advice) requests?
>>>/wsr/ , >>>/g/sqt , >>>/diy/sqt , >>>/adv/ , etc.
>carreer advice?
https://sciencecareergeneral.neocities.org/
>books?
https://spoon.wiki/Books
https://stitz-zeager.com/
>articles?
sci-hub.st
>book recs?
https://sites.google.com/site/scienceandmathguide/
https://4chan-science.fandom.com/wiki//sci/_Wiki
http://math.ucr.edu/home/baez/physics/Administrivia/booklist.html
>help with calculus?
https://spoon.wiki/WolframAlpha
>how do I post math symbols?
https://imgur.com/MDiglsS.png
>a google search didn't return anything, is there anything else I should try before asking the question here?
https://scholar.google.com/
>where do I look up if the question has already been asked on /sci/?
https://warosu.org/sci/
https://boards.fireden.net/sci/
>how do I optimize an image losslessly?
https://trimage.org/
https://pnggauntlet.com/

Question asking tips and tricks:
>attach an image
>if a question has two or three replies, people usually assume it's already been answered
>ask anonymously
>check the Latex with the Tex button on the posting box
>if someone replies to your question with a shitpost, ignore it

Stuff:
Meme charts:https://imgur.com/a/JY6NNeL
Serious charts: https://imgur.com/a/0qDEgYt (Post any that I've missed.)
Verbitsky: https://pastebin.com/SmBc26uh
Graphing: https://www.desmos.com/
Tables, properties, material selection:
https://www.engineeringtoolbox.com/
http://www.matweb.com/
>>
File: dfsdfsdfdsf.png (42 KB, 706x214)
42 KB
42 KB PNG
Do I ignore kinetic energy here since the block momentarily has a velocity of 0 at the top?
>>
There is no 2hu in the OP, but all is regular. I repeat: all is regular.

Unanswered questions:

Maths questions:
>>12333874 [No one solved it and got 35, so I'm placing it here.]
>>12339336
>>12339621
>>12342961 [Geometric motion is boomer speak for isometry. Also, he's talking about bidimensional space.]
>>12348297

Physics questions:
>>12332285
>>12332606
>>12340425
>>12346084
>>12347037
>>12349017 [Is anyone here in a really good mood?]

Biology questions:
>>12337484

Chemistry questions:
>>12345626

Engineer questions:
>>12347418
>>12348281

/g/ questions:
>>12335643 [Answered in the computer science general, also known as /mg/.]
>>12338151

Stupid questions:
>>12332999
>>12333746
>>12335153
>>12335155
>>12335349
>>12335816
>>12338785
>>12340528
>>12342264
>>12344142 [What?]
>>12348429
>>
>>12350480
Yes.
>>
f(x)=log_a(x) diverges for all a>1 because its inverse has solutions for all y=f(x). True or false?
>>
File: helpme.png (53 KB, 532x373)
53 KB
53 KB PNG
Bros. I can't do this excersize. They said I have to ignore "border conditions". Can somebody solve it? I have to hand it in tomorrow (wich is gay and retarded) and i also have 2 exams... Please bros
>>
>>12350608
I think the answer somehow is Ea=Eb Yb/Ya
>>
>>12350480
yeah or just consider it and it cancels out anyways.
>>12350556
makes sense but it's a complicated way of seeing it
>>
>>12350629
I can't unsee this way of spotting divergence but i dont know much about analysis. my claim would imply that sum_x{1/ax}=infinite for a>1 i think
>>
>>12350685
if it doesnt converge, it diverges (lol). it's a valid method i dindt know about
>>
What is the integral of [math]\oint_c \frac{1}{z-2}dz[/math] around the circle [math]|z-1|=5[/math]? The book says its [math]2\pi i[/math].

What I got:

moving to polar coordinates ([math]z=1+5e^{i\theta})[/math] I can rewrite the integral as
[eqn]\int_0^{2\pi}\frac{5ie^{i\theta}}{-1+5e^{i\theta}}d \theta[/eqn]
using
[eqn]y=e^{i\theta}\\
dy=ie^{i\theta}d \theta[/eqn]
but then my limits will be 1 and 1.

What I did wrong?
>>
You got isekai'd to another dimension. How do you test if it follows the same laws of physics as our dimension?
>>
>>12350783
can you just use the residue theorem? or is that what you're learning
>>
>>12350873
If I'm still alive it follows roughly the same laws as our dimension.
>>
File: word.jpg (33 KB, 180x180)
33 KB
33 KB JPG
>>12350873
> another dimension
> our dimension
>>
>>12350783
just evaluate the integral
>>
>>12350873
The first time you trip over see if you hand is magnetically attracted to the breast of the nearest female.
>>
>>12350419
I had a job interview, they said I was their #1 candidate, but that they would have to see what the 'hiring comittee' said about the matter first.

What does this mean?
>>
>>12351028
they're contacting your ISP to make sure you haven't posted on any neo-nazi imageboards
I'm sorry, anon.
>>
>>12351028
An extra stage of checks some firms perform. Anything from security, online, in depth references checks (which costs money hence not done for every candidate) to simply is there still money in the budget for the position or is the company now focused on another area.
>>
>>12351028
checking diversity quotas. It's hard out here
>>
>>12348281
For my electromechanics course at uni we use Electric Machines: Analysis and Design by cathey
>>
>>12351036
:(
>>12351050
I see. That's discouraging. Budgets during COVID are all fucked
>>12351053
No such thing where I reside, luckily!
>>
>>12347418
The emitter resistor changes the emitter voltage based on the emitter current. Thus the base emitter voltage changes based on the emitter current. Thus we have introduced feedback. The feedback helps to "stabilize" the transistor.

In mosfet's this is called a source degeneration rersistance.
>>
>>12332999
Arithmetics.
>>
File: 7674567.jpg (84 KB, 1136x783)
84 KB
84 KB JPG
>>12350419
Anyone bothered to explain alpha and beta errors in statistics?
>>
File: images.jpg (8 KB, 227x222)
8 KB
8 KB JPG
>>12333746
Go to a Doctor
>>12335155
Get Linear Algebra by Lang and read it cover to cover (no cheating) and do the exercises if you want to. You will be very powerful after that

>>12335349
Hyena's

>>12335816
Try simulating Schrodingers equation in 3 dimensions

>>12338785
It's 15 dollars / a month and it only makes you dumber so fuck off

>>12342264
In a limited capacity yes

>>12348429
Blood is produced in the bones if all the blood would stick to the bones you would die.
>>
>>12350783
>>12350783
[math]e^{i t}[/math] is a curve in [math]\mathbb{C}[/math] which winds around the origin counterclockwise. the parameter [math]t[/math] is basically angle. the complex logarithm should do the inverse thing: given a point on the circle it should give you the corresponding angle in the range [math][0,2\pi)[/math]. problem is that this function cannot be continuous. as you go around the full circle, the angle approaches [math]2\pi[/math], i.e. [math]\lim_{t\to 2\pi^-}\log e^{it} = 2\pi[/math]. but [math]\log e^{i2\pi} = \log e^{i0} = 0[/math]. however it works fine as long as you stay away from the positive [math]x[/math]-axis, which is exactly where [math]0[/math] and [math]2\pi[/math] meet as angles.
your integrand has primitive [math]\log\left(-1+5e^{i\theta} \right)[/math] but only on [math]\mathbb{C}[/math] without the "positive [math]x[/math]-axis emanating from -1". so it works fine if you don't integrate over a full circle, but only around an arc which misses the point [math]-1 + 5[/math]:
[eqn]\int_{0+a}^{2\pi - b}\dots = \left[ \log(-1+5e^{i\theta})\right]_{0+a}^{2\pi-b}[/eqn]
this formula holds for every arc missing the mentioned point. you'll get the integral over the full circle if you connect the boundary points, i.e. send [math]a \to 0^+[/math] and [math]b\to 0^+[/math] while keeping in mind that [math]\lim_{t\to 2\pi^-}\log e^{it} = 2\pi[/math]. you should get 2pi.
>>
>>12350608
REEEEEEEEEEEEEEEEEEEEEEEEEEE WHY IS NNOBODY REPLYING
>>
>>12351164
because I hate displacement fields with a passion and I don't want to refresh on that stuff only to be able to answer a question that looks like it was written by a question-writing AI with dyslexia.
>>
File: untitled.png (1 KB, 195x202)
1 KB
1 KB PNG
I'm lost in graph theory language, any pointers to particular algorithms/problems that are applicable greatly appreciated
or just the correct formulation of words to learn more

bipartite graph, no parallel edges
degree distribution of red nodes given, bipartite so these edges are all red <-> blue

blue nodes have a total, say 100
red nodes have a weight, edge of red <-> blue node weight is subtracted from total
blue node total >= 0

weight for edge to any blue is constant
cost of red <-> blue1 = 5
is the same as red <-> blue2 = 5

for example
red node degree dist (1, 1) with weights (2, 3)

blue nodes with total (5, 3)

what sort of problem is this? any pointers to specific terms ?
right deficient matching?

a follow up if you're up too it - whats the quickest way to validate if given red node degree distribution, weights, blue node totals
but no edges, that there exists a valid solution

i feel like it's just some dynamic programming solution or integer programming but i felt putting it in graph theory terms
there might be something smarter and analytical
>>
>>12351430
To elaborate - we cant have the weights of edges to blue nodes sum greater than a node property of blue
>>
>>12351109
Good post.
>>12351430
Do you mind asking your question in english instead of schizospeak?
I can't read this.
>>
>>12351455
Apologies, I'll try again.

I'll explain the problem in english, now i hope my schizio makes sense

People want unique dinners. Different people want a different number of unique dinners, some want 4 different dinners, others 2.

For each dinner, there is a varying number of portions each person wants, some want 2 portions of 4 different dinners, others want 4 portions of 2 different dinners.

We have a stock of portions for each dinner.
Given the number of portions of each dinner, and what dinner demand is - is there a valid solution

Remember - each person must have a set number of portions from x different dinner options.
>>
>>12350419
Whats the sense of the standard evistion formula?

It just looks like the mean of errors but skewed upwards because the denominator is under square root (I simplified it, since the numerator is squared I apply the square root to both and it just becomes the sum of all errors, converted to positive by being squared and then square rooted, divided by the number of measures under square root) I dont get the sense, would a normal average error be better? (With absolute values in the numerator to not have 0)
>>
>>12351495
It reminds me of hashing the most. I'd recommend copying cuckoo hashing.
It also looks like https://www.sciencedirect.com/topics/computer-science/allocation-problem , and I've found the keyword "Object Allocation Problem."
>>
Hi /sqt/
Tourist here hoping for some help with my finance homework. Just to clarify: the problem is already completed I just would like help understanding where the value 5256.28 comes from.

I thought FCF6 is supposed to be 3507(1.075)^6 = 5412.36 but that is wrong and following through the equation with that number gives a value outside of the 10% margin for error.

Also, I'm confused on which values should be used to calculate the NPV using a time-value of money function on the TI-84.
N = 5
I = 10%
PV = (solve for)
PMT = 0
FV = 99572.18(???)
Are the values that I use but these are clearly wrong.

I know how to do this calculation by hand, but that is incredibly time-consuming and the upcoming exam that might cover this material will be timed.
Help would be greatly appreciated.
>>
>>12351659
Niggy I'm not a magician, what do the letters mean?
>>
File: MGFM homework.png (1.05 MB, 1769x831)
1.05 MB
1.05 MB PNG
>>12351659
Forgot my pic, sorry.
>>
>>12351663
N is the Number of periods, in this case 5 years
I is the Interest rate, in this case the WACC of 10%
PV is the Present Value of all the periods valued at that interest rate.
PMT is the amount paid per month, like dividends or rent payments, this problem doesn't have any.
FV is the Future Value, which should be the combined value of the Cash Flows (CF).
>>
>>12351659
use excel
>>
File: mml.jpg (43 KB, 342x500)
43 KB
43 KB JPG
what do i read after pic related?
probably don't want to pursue ML in grad school but i want enough domain knowledge to follow papers
>>
>>12348281
polite bump!
>>
>>12351712
I'm not going to be able to use excel on the exam because the test requires a lockdown browser.
Also, the NPV excel function doesn't give the same value here >>12351665 even accounting for 10% margin for error.
>>
>>12351805
Wait no, the excel function does work with a 10% margin for error, but it's too close for comfort.
>>
>>12351777
oh shit im sorry i didn't see >>12351069, thank you very much anon
i could always use more though!
>>
I have a knapsack problem as such:
>each item has a set of n values in n different category [math][v_1, v_2, ..., v_n][/math], some of which are negative
>each item has the same weight
>there is a n-element vector [math][k_1, k_2, ..., k_n][/math], with weightings for each category
>I want to minimize [math]\sum k_n log(\sum v_n)[/math], the weighted average of the logarithm of each category
I can encode each item as a binary variable, but brute-force is intractable for large n (>100k)

Would greedy search work here? What are my options?
>>
>>12352001
For a greedy search, I suppose I could compute [math]Dsum / Dv_n[/math] for each column, but that seems ugly as hell.
>>
Posting same question from previous thread.

Could someone please explain the concept of entropy to me? I just don't understand it... my current understanding is firstly that its 'disorder' but that isn't really useful for understanding what it represents numerically. I think it can be thought of as the potential useful work available from a heat(?) source, where a higher [math]\Delta S[/math] means there is less potential work available. Is this correct? If not, please articulate it to me.
>>
>>12352017
maybe it's helpful to think of it in terms of boltzmann's definition: [math] S = k_B ln(W) [/math], where kb is boltzmann constant and W is the "number of microstates" (see: https://en.wikipedia.org/wiki/Microstate_(statistical_mechanics) )
you can think of disordered systems as having a larger number of microstates, corresponding to all of the ways that you can achieve that type of system. for example, if you have a collection of spins, all of them aligned in one direction can only happen one way, whereas an even mixture of up and down can happen in many different ways.
>>
it's 25
>>
>>12352059
Thanks, the micro/macrostate definition was never covered in my thermo course and is new to me. What I am trying to get at is how I can think of entropy in terms of heat within a thermodynamic system. For example, in a diesel cycle process 2-3 (constant pressure heat addition), what does the increase in [math]S[/math] represent? If you could explain this in terms of micro/macrostates I might have a better understanding.
>>
Anyone got good alternative recommendations to khan academy? I fucking hate khan academy.
>>
>>12351088
Null: Boring result, what the researcher is looking for evidence to reject. The meds don't do anything or worse, average crop yield is no better than control, no reason to believe median cholesterol lowered, etc.

Alternative: Desired result, what we want to find evidence for usually, although this type of thinking can be dangerous in science. Medication improves survival probability, average yield is higher than control, median bad cholesterol decreased with use of pill. You have to use weasel words in technical writing but people usually get it.

Rejection region: If the stat lands here, reject the null in favor of the alternative. Ideally determined before the experiment by theory or prior data. Usually extreme in some sense, like if we want to show evidence that the population average is larger than some value, we have evidence to that effect if the sample average is much larger than the specified value. The theory is where we get more specific and prove certain methods are 'best.'

Alpha: Probability of hitting the rejection region, and rejecting null given null is true. A bad result, want alpha small like .05 or lower.

Beta: Chance of missing the rejection region given the alternative is true. Almost always the case but a bad result, how bad can vary depending on how far the truth is from the null.

Power analysis can involve figuring out how small a deviation from the null you want to detect with chance 1-beta, how big a sample you may need to do that or better. In your pic the alternative average is big enough to the point where beta is fairly small, for example. But that's a meme.
>>
File: Circuit1.png (29 KB, 574x380)
29 KB
29 KB PNG
Does anybody know the name of this circuit? At first glance it's a common emitter with an active load and active bias, however I am told it has a special name. It has somethig to do with load curves, that's all I know.
I'd appreciate any help. The gain is around 0.6 with a 2k2 load and around 0.2 with an infinite load (that is, open circuited), and R1=R2 in both cases.
At first my theory was that it was some sort of programable current source, controling the R1 and R2 ratio to determine how much of the current sourced from the up mirror is sinked in the lower one. But I can't find any info online about it.
Thank you
>>
File: Capture.png (354 KB, 1685x199)
354 KB
354 KB PNG
>>12350419
I get 5.65 for the velocity, but the angles sum to 110?
Is my professor fucking with me
>>
question about nuclear physics
excited states are labeled $J^\pi$
J = spin
$pi$ = parity

but I have seen excited states labeled with a subscript as well, for examples $2^{+}_{1}$
what does the subscript mean?
>>
>>12351725
I think that should be enough, or at least as good as you can do without just retreading the same stuff over and over. I don't think there are any books out that cover the stuff between there and the state of the art because it's a moving target and no-one wants to write book that's obsolete the day it goes to print.
>>
>>12350419
help with proof pls, where do I start??

Let [math]V[/math] be a finite dimensional vector space. Let [math]T \in \mathcal{L}(V,V)[/math]
Prove that for all [math]\epsilon >0[/math] and all [math]\lambda \in \mathbb{R}[/math] there exists [math]\alpha \in \mathbb{R}[/math] with [math]|\alpha - \lambda| < \epsilon[/math] such that [math]T - \alpha I[/math] is invertible.
>>
>>12352732
Could you please show your working?
>>
>>12352771
I'm probably one of the few people qualified to talk about this but I want to make sure I know what you're asking since I'm a little lost. And since notation varies wildly by subfield.
What type of state are you representing? The excited state of a nucleus?

My best guess is that the subscript is orbital or total angular momentum. Since excited nuclear states may have different angular momentum from their ground states.
>>
I have an assignment to do on linear regression. Have to extract the data, make some analysis based on it, plot it, all of that stuff.

Problem is, I have no fucking clue of what subject should I choose. I have to make the sample (probably with a google formulary or something like that), so I can't just grab some data from the internet from any given random subject and do the analysis. Any ideas of something more or less doable here? I only came up with very simple, dull and dumb things like the correlation between hours studied and your notes but that's so fucking obvious. It's just that I have no idea of what could I ask to random college students. The subject can be anything I suppose, but it shouldn't be too polemic and it should allow me to fit a linear regression
>>
Is writing in a notebook really that important for learning? The whole learning from home thing has me writing less and less and relying on pds and powerpoints more and I don't know if it's a good idea or not.
>>
>>12353522
Learning is about reinforcement and the like, so writing down notes itself might not be helpful if you are not really thinking about what you are writing down, but recreating notes, making your own good notes might help.
>>
>>12353522
I take notes so that when I'm done I can go verify that I've actually done something. It's far too easy to just scroll through pdfs without actually thinking about the content at all. Writing what you think is important and then reading it again at the end give you two repetitions you otherwise don't bother with and while I definitely can't prove that that matters it does feel important to me.
>>
>>12353522
It's not about the notes themselves so much as about engaging you with the content. When you write something down, you're more likely to stop and think.
>>
>>12353389
Could you do physical phenomena? Hooke's law is a nice linear relationship, and gathering data should be a breeze.
>>
>>12353389
"How far away do you live" and "how long does your commute take" is simple and nonthreatening, has a clear interpretation for regression and you can break it down by mode of transport if you need to hurf blurf a lot. This might not work if you're in a shitty situation with covid and no-one's commuting anywhere though.
>>
>>12352968
I dont find this question very clear anon. Provide context
>>
I'm currently reading Algebra by Artin. This is my first time going through a math book on my own. Is it normal to have to re read some sections over and over again until I understand them? It seems like I keep getting stuck on a proof or concept he is talking about. So far, I've been able to figure it out, but I'm only near the beginning of the book. I imagine that when I get much deeper into the book, I may not be able to understand what he is talking about.
>>
>>12352968
for T=0 this is obviously true. If T=/=0 do it by contradiction and use the fact that T has finitely many eigenvalues.
>>
Proving a surjective function has a right inverse without using the axiom of choice.

So, I was bored today and came up with this:
Let [math]f:A \to B[/math] be a function with no right inverse. This means that for every function [math]g:B \to A[/math] there is some [math]y \in B[/math] such that [math]f(g(y)) \neq y [/math] (*). Suppose that there is some [math]x \in A[/math] such that [math]f(x)=y[/math]. Then define [math] h:B \to A[/math] as [math]h(b)=x[/math]. Since (*) holds for [math]h[/math] then [math] y = f(x) = f(h(y)) \neq y [/math]. Thus, [math] f [/math] is not surjective. By contrapositive, we have proven that if a function is surjective, then it has a right inverse.
The problem is that I've heard about a million times that proving this requires AC, which means I've either used it without realising it or fucked up the proof somewhere. So, could you tell me where?
>>
I was stung 13 times by bees over 2 weeks with no reaction at all besides the slight pain, on the 14th sting I broke out in hives which lasted for about 25 minutes, now whenever I get stressed I break out in hives in the same place that they first appeared. Should I be worried about this? I will be stung again many times.
>>
>>12350608
>lenght
lol
>>
>>12353998
Never mind, I see where I fucked up. I'm confusing [math]\forall g \exists y[/math] with [math]\exists y \forall g[/math].
>>
p2p live streaming ?
>>
File: Capture1.png (51 KB, 1476x894)
51 KB
51 KB PNG
>>12353044
>>
>>12354021
>I will be stung again many times.
bee stings are sensitizers, sounds like you've been sensitized.
>>
File: 1603061136521.jpg (3 KB, 125x125)
3 KB
3 KB JPG
place on 4chan for astronomy/telescopes?
I'm 20 and landed an internship that's gotten me more money in the last three weeks than my shitty summer job did in 3 months.

I've always wanted to get a telescope, and now I have the money. Is there a place on 4chan for home astronomy?
>>
Heyyyy guys, any 'philosophy of science' books recommendations?
>>
How can I convert repeating decimal to binary?
For example 0.(3)[b10] in binary?
I know how to do normal fractions, or repeating fractions in bases in the same power (for example [b2] to b[4]), but I don't know how to do this one.
I mean the method, without using the calculator
>>
>>12354658
The method I'm trying is to set 0.(3) as x
then say that 9x = 3 = 11[b2]
so x in binary = 0011[b2]/1001[b2]

But is there a method without long division?
>>
Let [math]p[/math] be prime and consider the cyclic permutation [math]\sigma = (1,2,\dots,p-1,p)[/math] in [math]S_p[/math]. Then for all [math]1 \le k \le p[/math] we have [math]\langle \sigma \rangle = \langle \sigma^k \rangle[/math].

Forgive my incredible stupidity, WHY? Exactly what role does the primality of [math]p[/math] play here?

(My question is more about number theory 101 than about permutations and groups, I suppose)
>>
>>12354689
<sigma^k> is clearly a subgroup of <sigma>. as such, its order must divide the order <sigma> which is p. only divisors of p are p or 1 by primality.
>>
Can the volume of a solid of revolution be 0?
>>
>>12354841
yes, if it degenerates to something two dimensional
>>
should i use mometasone furoate or fluticasonpropionat and azelastinhydrochlorid to treat runny nose caused by allergies?
>>
let's suppose an object moves having initial and final kinectic and potential energy, if friction is negligible then Ui+Ki=Uf+Kf
but if I have friction or any other type of non conservative force I would have Ui+Ki=Uf+Kf+Wnc
which gives deltaU+deltaK=-Wnc=deltaE
but I know that Wnc=deltaE so what am I doing wrong?
since energy is not lost only transformed, then the energy dissipated by non conservative forces shold be take into consideration.
am I doing something wrong?
>>
>>12355042
Nothing wrong except you are forgetting the fact [math]\Delta E[/math] will be negative, the system loses energy due to friction.
>>
>>12354658
>>12354666
Any repeating decimal is a rational number. So let x=a/b. Find the least n s.t. 2^n≡1 (mod b) => 2^n-1≡0 (mod b), i.e. 2^n-1 is a multiple of b. (2^n)*x = (2^n)*(a/b) = (2^n-1)*(a/b)+(a/b) = k+x where k is an integer. IOW, the binary representation of x repeats every n bits, with those bits being the binary representation of the integer k.

A repeating decimal can be converted to a fraction using the formula for the sum of a convergent geometric series. If d is the integer formed by the digits which repeat and n is the repetition period then x = d/(10^n-1). E.g. x=0.428571428571428571... = 428571/999999 = 3/7. To cancel fractions, use the Euclidean algorithm to find the GCD.
>>
What do I do when I get a question wrong on textbook problem sets? Am I supposed to study how I got it wrong? Give up and cry? Re-read the chapter before doing the rest of the problems?
>>
>>12356183
depends on why you got it wrong
oftentimes for me if i thought i got it right then got it wrong anyways it's because i was sloppy. if i got it wrong because i literally had no idea how to do it properly then that kinda hurts but that's either just lack of knowledge or lack of pattern recognition?

t. brainlet who can can barely remember any of the formulas or procedures for linear algebra

>Give up and cry?
that's my strategy!
>>
FUCK jupyter notebooks, i'm running a thousands of entries long for loop that requires input at every iteration, so i've been inputting meticulously at every iteration. Then one time i type "1" while clicked out of the input textbox and it goes to fucking markdown mode on the cell and my output disappears and the input box goes with it so i can't continue entering info even if i change the stupid fucking cell type back to code

is there any save or to i have to start over? i can't save the variables using a different cell with "%store varname" since the cell with the loop is still technically running. but i need to access its output box which has the input textbox inside it to continue. help
>>
>>12356386
do you have to use Jupiter notebooks? what about iPython? what if you make the for loops generator functions and save every iteration. the generator function will save your place even if the cell fucks up
>>
>>12356492
i don't have to use jupyter but it's what i'm in at the moment. i can add ways to save the data at every iteration but it would require restarting the kernel/exiting jupyter and rerunning it, to get it out of it being stuck. my question is, is it lost and do i have to do that?
i'm still sitting with it in code mode, with that kernel running, waiting for a way to get the output back
>>
File: impossible.jpg (370 KB, 1552x1369)
370 KB
370 KB JPG
>>12333874
it's impossible friend
dimensions in parentheses mean they are constrained by others to be exactly that
>>
>>12356512
just type your input into a txt file so you can reuse it and just read it with your script?
>>
There's this job that I found posted today from a pretty well known company.
Would it be too late to apply 2 days from now? I want to get my cover letter checked, but I'm getting a little impatient and want to send it now just in case I miss out.
>>
I don't actually have anything to say, I just want to post this Remilia.
>>
File: metal alloy.jpg (51 KB, 600x600)
51 KB
51 KB JPG
for the mineralogists and thos who just love metal.
I did not want to make a own thread for it.
>>
>>12356737
cool rocks anon
>>
>>12356663
Job openings typically stay open for weeks to months, depending on how bad they want it filled.
>>
Based anime-poster. I'm the one who asked about the cyclic module with a non-cyclic submodule. An anon said [math]\prod_n \mathbb{Z}[/math] with [math]\bigoplus_n \mathbb{Z}[/math] works but I don't think that's right as I don't particularly see the generating element for [math] \prod_n \mathbb{Z}[/math].
>>
>>12351725
It really depends on what you're most interested in. Some fields don't use much math while others can get fairly involved (e.g. manifold learning or some bayesian stuff). At the most generic level, learning more probability, mathematical statistics, and linear algebra is super helpful. Check out Michael Jordan's list of books that he thinks are most important for ML

analysis isn't directly as useful, but for me it was the most important piece of being able to read research papers well. mathematical maturity and all that.
>>
>>12352494
mit ocw

>>12354365
Kuhn's structure of scientific revolution is a standard intro text. Just check the syllabi from schools with good analytic philosophy programs (all top schools in the west)
>>
>>12357429
>he actually came here to ask
Wew, rare.

Anyhow:
Any ring with identity [math]R[/math] that isn't a PID works, because a ring with identity is a cyclic module over itself (generated by the identity) and admits a non-principal ideal (which is the same as a non-cyclic submodule).
I particularly recommend using the clasical example [math]R=M=\mathbb{Z}[x, y][/math] and the non-cyclic submodule [math]\langle x, y\rangle[/math].

No idea what the lad meant with the Z products thing.
>>
>>12357720
Forgot to specify that the ring has to be commutative, otherwise you don't have the equivalence left submodule - left ideal - ideal.
>>
What is your field of study and what motivates you?
Joined the army to help pay for college and seeing military tech is interesting but i feel like my old goals are dead and i need to find new ones.
>>
I'm studying CS and getting really frustrated at all the outdated and irrelevant shit they're making us learn. If I dropped out and just self learned I would have acquired 10 times better knowledge and skills, but would not have a degree (and would lose my scholarship).
Is it worth it putting up with this pile of bullshit and wasting so much time on nothing just to get a degree?
>>
What sort of maths do you need for basic chemistry?

What about basic neuroscience?
>>
How can I do the contour plot of [math] f(x,y) = 1 - x^{2}, x \geq 0, y \geq 0 [/math] and [math] x + y \leq 1 [/math] in latex?? I read the documentation but didn't find how to plot using the inequation
>>
>>12350419
What if you smash a sun made of fire into a sun made of ice? What happens, /b/?
>>
>>12357956
Part of the reason jobs only look for people with a degree is for exactly that reason. It shows you have the dedication to follow through on a task even if you do not always enjoy it or think its retarded, precisely what you'll experience in a CS role.
>>
>>12357972
>What sort of maths do you need for basic chemistry?
cancelling units
fudging yields
"i think I might need a 200% excess of this reagent"
>>
>>12357972
addition, subtraction, multiplication, division
add fractions if you're going for PhD
>>
>meaning that any finite subcollection
of these random variables are independent
How come it's stating finite specifically? Wouldn't the independence also apply to infinite ones?
>>
>>12358108
Can't take an infinite sum
>>
>>12358108
Nyet.
>>
>>12358133
>>12358148
Sorry to ask, but why not?
>>
>>12358162
If the mean of the distribution is non-zero then an infinite sum of the values will always tend towards +/- infinity. [math]Y=\infty[/math] is bad mkay.
>>
>>12358180
thank god, I was expecting something like
>it's an infinite process that will never finish so you will never know the result
>>
>>12358180
But the value of Y doesn't matter, as long as all of Y still has a probability of 1, no? And Y's value doesn't affect the independence, does it?
I feel like I am missing something very basic here, sorry
>>
>>12358199
Because Y would always be [math]\infty[/math] no matter the distribution of the X variables, independent or otherwise, which contradicts one of the assumptions.
>>
is inf A = min (argmin A) ?
>>
>>12358192
That's true though. Infinite sums are meaningless without some notion of convergence.
>>
>>12358348
what's argmin A? assuming A is a set, not a function
>>
I am totally blackpilled... I thought Fran Blanche was an actual, smart, STEM engaged female
>look bio
>it's a tranny
>>
>>12358219
Oh, now I get it, many thanks!

>>12358348
Not sure how that argmin works, but infimum doesn't have to part of the set you're looking at
>>
grouplet here. let [math]D_n[/math] be the dihedral group of an [math]n[/math]-gon (i.e. [math]\vert D_n \vert = 2n[/math]), generated by rotation [math]r[/math] and reflection [math]s[/math]. suppose [math]n[/math] is even. I need to show that [math]H = \langle s, r^{n/2} \rangle \trianglelefteq D_n[/math]. I've shown that [math]H[/math] is closed under conjugation by [math]s[/math] (using [math]sr = r^{-1} s[/math]), but I'm struggling to show that it's closed under conjugation by [math]r[/math].

hints are much appreciated!
>>
Should I eat stood up?
>>
File: momE.png (88 KB, 415x647)
88 KB
88 KB PNG
When I solved this before peeking at the solution, I just did [math]J = m\DeltaV [/code]. What implied that the vectors must be broken down into components first, and must that always be done?
>>
>>12358522
There are explicit formulas for computing products in Dn, you know.
>>
What is the pressure in the center of the Earth?Very huge, because center of the Earth? Or zero, because pressures from all directions cancel each other?
>>
>>12358522
>>12359081
I'd like to show that if [math]h = sr^{jn/2}[/math] for some [math]j \in \mathbb{Z}[/math], then [math]rhr^{-1} = h[/math] (which must be the case if [math]H[/math] is normal). using the explicit formula [math]s^a r^b s^c r^d = s^{a+c} r^{d + (1-2c)b}[/math] I arrive at [math]rhr^{-1} = sr^{jn/2 - 2}[/math], but this is not in general an element of [math]H[/math], as [math]r[/math]'s exponent is not a multiple of [math]n/2[/math].

what am I missing? I've gone over the calculations so many times
>>
>>12359054
J=m(vf-vi) is there in the text. But you're given two vectors in polar form, and to get their sum or difference in either polar or Cartesian form requires converting the individual vectors to Cartesian components, adding (or subtracting), then (optionally) converting the result to polar form.
>>
>>12359150
Pressures don't cancel like that. Inward pressure cancels outward pressure, not inward pressure from the opposite direction. The pressure would be very high.
>>
File: 1604174887751.png (6 KB, 329x318)
6 KB
6 KB PNG
ESL here.
How is this method of addition called in English? I can't translate it from my lang
>>
File: Untitled.png (3 KB, 456x107)
3 KB
3 KB PNG
yo where the FUCK can I get this integral evaluated?
my professor said to use an online calculator and none of the 3 I tried were able to compute it
this is some bullshit
>>
>>12359276
epsilon and c are constants btw
>>
>>12359282
next you'll tell us that cos is actually the cosine function.
>>
>>12359276
No dice.
https://math.stackexchange.com/questions/117536/evaluate-int-cos-cos-xdx
>>
>>12359189
thanks i don't know why i thought I could just do arithmetic on the magnitudes without breaking into components first..
>>
How does Latex's newcommand work?
I would explain the issue I'm having, but 4chan's filter is being a whiny pussy.
>>
>>12359496
It acts like a shell script 'alias' command or a very simple function definition. You'd almost never have to use it unless you are creating your own style document or want to simplify multiple other commands you find yourself using over and over again.
>>
>>12359521
>It acts like a shell script 'alias' command
That's what I thought too, and it's almost correct.
Being curt, I wanted to make a command for \begin{equation} \begin{split} and the corresponding closing of the split and equation, but Latex doesn't finish all the Macros and then compile, it does things in some sort of stupid order which stops this from working.
See https://stackoverflow.com/questions/3883789/latex-newcommand-for-endverbatim-et-al-not-working
>>
File: CREquation.png (36 KB, 1354x226)
36 KB
36 KB PNG
Can't seem to think of how to solve this even though it appears to be so simple.
>>
File: 1605727325483.png (59 KB, 634x442)
59 KB
59 KB PNG
How do I prove b?
>>
I'm doing linear algebra. Is there a good list of things like "If an nxn matrix has a non-zero determinant then it is invertible"? Basically good rules that will help me quickly identify how to prove something if I need to in an exam
>>
how are idempotent elements going to help me find a ring isomorphism?
>>
>>12359570
Feel free to assume any two points in the domain can be connected by a smooth curve.
>>
the fuck is the difference between tensors and arrays
>>
>>12359632
wikipedia is strong as fuck for quick math checks and lists of definitions and theorems
>>
>>12359764
tensors are mathematical objects with well defined transformation properties. it just happens that you can trivially represent a rank-1 or rank-2 tensor with a vector or a matrix / array. however higher ranks or multi-index tensors how no equivalent representation.
>>
Does time travel preserve energy? If I go back to 1920 aren't I just redistributing a bit of energy to another place on the manifold? Sure there are local discontinuities when a person arrives or leaves, so to speak, but there's the same amount of 'stuff' sub specie aeternitatis, right?
>>
Im looking for a comprehensive book about human decomposition and why, how and when flesh changes colour after death.
Anyone has any suggestions?Idk if this is the right board to ask.
>>
>>12359829
You are making two false assumptions. Firstly that time travel is possible. Second that energy is conserved across the entire universe. Nothing in GR says that, in fact it can't be true because of dark energy.
>>
I need to prove the following isomorphism for a problem I am working on. I need to show [math] I\cdot (R/J) \cong (I+J)/J[/math]. I know, by the second isomorphism theorem, that [math] (I+J)/J \cong I/(I\cap J) [/math] but I don't really know if that helps me here. Is there a way to solve this problem without making an explicit isomorphism?
>>
>>12359235
I don't think I've ever heard it named. I'd just say "written addition" or if I'm feeling fancy "long addition" alluding to long division.
>>
File: hi-c map.png (333 KB, 685x608)
333 KB
333 KB PNG
Biofags, how am i supposed to read Hi-C maps?
What i understand:
>Deeper red = higher probability of contact
>Squares = Associated domains (Genes, TADs, sub-TADs depending on resolution)
>Dots atop of the squares = Loops
What i don't understand
>If X and Y axis both represent bp distances in the same sequence then how do i interpret the values relative to each other? I.e if i see a red dot representing a loop at X = 20Mbp and Y= 10Mbp do i interpret it as a distance of 30Mbp between the ends of the loop?
>How should i see stripes (in a 3D sense) and why do they appear assymetrically at the edges of TADs?
>>
if we have a system of equations a=b and c=d, can we multiply one by another, to get ac=bd?
>>
>>12360121
If a=b and c=d, then ac=ad=bc=bd. IOW, given ac, you can replace a with b or replace c with d or both. It's probably not helpful to think of it as multiplying two equations, though.
>>
I accidentally punctured an old lithium ion phone battery, used a magnetic screwdriver. Tiny amount of smoke that lasted about a second, no fire or swelling. Only one spark and that was when I touched the screwdriver to the puncture. I’ve put the battery in a metal biscuit tin and left it outside in the rain.

Anyone know if the battery is likely to cause me any harm when I open the biscuit tin in the morning? Don’t want it to explode and blind me or anything
>>
>>12360252
ok, thanks, I did so much algebra today I started questioning the most basic things
>>
>>12360121
>>12360331
lol yeah you cna do literally any operation there. eg: a^c=b^c=a^d=b^d, the big principle behind this is replacement of equivalent expresions
>>
>>12359598
are you going to special ed college or what?
+(A)=(A)=A this proves all your shit
>>
>>12359570
i dont know that principle. just integrate bro
>>
Why does this not have a basis? [eqn] {(a,b,c) : a-3b+c=0, b-2c=0, 2b-c=0} [/eqn]
>>
>>12360705
It's equivalent to {(0,0,0)}.
b=2c, c=2b => b=c=0
a-3b+c=0 => a=0
IOW, the solution space is 0-dimensional.
>>
Let [math]f: \mathbb{R} \to \mathbb{R}[/math] be measurable. Suppose [math]f(\mathbb{R})[/math] is a Borel set, and for every real interval [math](a,b)[/math] we have that the preimage [math]f^{-1}((a,b))[/math] has positive Lebesgue measure.
Is it possible that [math]\mathbb{R} \setminus f(\mathbb{R})[/math] has positive measure?

I think it is possible, but I'm struggling to find an example for such [math]f[/math]
>>
>>12360414
>>12359598

Question looks dumb but its difficulty depends on how much rigour is expected here. If you are allowed to take [math](x)=x[/math] for granted, then you can just use
[eqn]\left(\sum_{j=1}^{k}a_j\right)= \sum_{j=1}^{k}a_j[/eqn].
For b, you have to prove that if the summation is valid for n, then it is valid for n+1 for all n. In b, you can cancel out the first k terms using a, then claim that the remaining terms are equal for all n by taking out the parentheses. I dont know the context here so it might be too informal
>>
>>12361176
Let A be dense open set in R with finite measure. Define f(x)=x if x is in A, 0 if x is not in A.
>>
Hi, anon,
I hope, I understand how does the Bayesian updating work when we have evidence E, but I don’t know to update it if we have the opposite of the evidence - E. In other words, how to lower our confidence about the hypothesis?

Let's imagine that we are at war (yes, it’s me again with military examples).
[math]P(H) [/math]- the probability that there is a sniper at the enemy side. It is 1/1000 (on each 1k of soldiers there is 1 sniper)
[math]P(E|H)[/math] - probability of the hit if the sniper makes a shot. Let it be 0.95.
[math]P(E)[/math] - probability of the average hit at modern warfare - 0.5.
H for hypothesis, E for evidence

1. Given that there was one deadly shot that killed Kenny, how does our belief that it was a sniper change?
[math]P(H|E) = \frac{P(E|H)P(H)}{P(E)} = \frac{P(E|H) P(H)}{P(E|H) P(H)+P(E|\neg H) P(\neg H)}[/math]
Also a question:
I expand [math]P(E)[/math], the part [math]P(E|H)*P(H) = 0.001*0.95 = 0.00095 [/math], so [math]P(E|\negH)P(\negH)[/math] must be equal to 0.5-0.00095 = 0.49905. [math]P(\negH)[/math] is 999/1000 = 0.999. And if I’m right [math]P(E|\negH)[/math] is NOT [math]1 - P(E|H)[/math], because it made the probability of the shot, given that it is not made by a sniper, as 0.05 and this does not look okay. Does it?

So it is calculated as [math]\fraq{P(E|H)P(H)}{P(\negH)}=0.49905/0.999=0.49954954955[/math]

Then, [math]P(H|E) = \frac{P(E|H)P(H)}{P(E)} = \frac{P(E|H) P(H)}{P(E|H) P(H)+P(E|\neg H) P(\neg H)} = \frac{0.00095}{0.5}=0.0018[/math]


2. Another shot and another Kenny is dead.
[math]P(H|E) = \frac{P(E|H)P(H)}{P(E)}=\frac{0.95*0.0018}{0.5}=0.00342[/math]

Etc.

But what if the second shot was a miss? How to decrease our posterior probability, knowing this fact?
>>
Sorry, here is a fix:

Hi, anon,
I hope, I understand how does the Bayesian updating work when we have evidence E, but I don’t know to update it if we have the opposite of the evidence - E. In other words, how to lower our confidence about the hypothesis?

Let's imagine that we are at war (yes, it’s me again with military examples).
[math]P(H) [/math]- the probability that there is a sniper at the enemy side. It is 1/1000 (on each 1k of soldiers there is 1 sniper)
[math]P(E|H)[/math] - probability of the hit if the sniper makes a shot. Let it be 0.95.
[math]P(E)[/math] - probability of the average hit at modern warfare - 0.5.
H for hypothesis, E for evidence

1. Given that there was one deadly shot that killed Kenny, how does our belief that it was a sniper change?
[math]P(H|E) = \frac{P(E|H)P(H)}{P(E)} = \frac{P(E|H) P(H)}{P(E|H) P(H)+P(E|\neg H) P(\neg H)}[/math]
Also a question:
I expand [math]P(E)[/math], the part [math]P(E|H)*P(H) = 0.001*0.95 = 0.00095 [/math], so [math]P(E|\neg H)P(\neg H)[/math] must be equal to 0.5-0.00095 = 0.49905. [math]P(\neg H)[/math] is 999/1000 = 0.999. And if I’m right [math]P(E|\neg H)[/math] is NOT [math]1 - P(E|H)[/math], because it made the probability of the shot, given that it is not made by a sniper, as 0.05 and this does not look okay. Does it?

So it is calculated as [math]\frac{P(E|H)P(H)}{P(\neg H)}=0.49905/0.999=0.49954954955[/math]

Then, [math]P(H|E) = \frac{P(E|H)P(H)}{P(E)} = \frac{P(E|H) P(H)}{P(E|H) P(H)+P(E|\neg H) P(\neg H)} = \frac{0.00095}{0.5}=0.0018[/math]


2. Another shot and another Kenny is dead.
[math]P(H|E) = \frac{P(E|H)P(H)}{P(E)}=\frac{0.95*0.0018}{0.5}=0.00342[/math]

Etc.

But what if the second shot was a miss? How to decrease our posterior probability, knowing this fact?
>>
>>12361234
Thanks anon!
>>
>>12361391
If you have a set of event samples [math]y_1,y_2,...,y_N[/math] the probabilities become conditional on all previous events, at which point you have to make assumptions about the so called memory of the process, in the form of multidimensional joint probabilities.
>>
>>12361415
Sounds pretty hard, but interesting. Have you any article about it?

The problem is that collecting only the evidence that makes us believe more in our hypothesis is a mistake. We must take into consideration those that contradict it. And I could not found any simple examples of it.
>>
>>12361462
Just read any proper book about bayesian stats, basics are covered by all. Look into the concept of conjugate priors. For interesting applications look into bayesian filtering books and bayesian estimation of Markov processes.
>>
>>12361502
Thank you!
>>
>>12361234
>Let A be dense open set in R with finite measure
example of such set?
>>
>>12361595
Let q_1,q_2, ... be the enumeration of rational numbers, define I_n=(q_n-1/2^n, q_n+1/2^n) and set A to be the union of all I_n's. A is open as a union of open sets, A is dense since it contains the rationals, and A has finite measure, since the measure of A is smaller then 1.
>>
>>12361606
Sorry, smaller then 2.
>>
>>12361606
right, the ol' 1/2^n trick
>>
>>12361646
If you want to have an open dense set A with a prescribed positive measure m, i.e. |A|=m you can also construct it. Write m as a series of positive numbers a_n, [math]m=\sum_{n=1}^\infty a_n[/math]. For each n let I_n=(n-1,n) and each I_n construct a fat cantor set C_n with measure 1-a_n/2. Then D_n= I_n\C_n is open and dense in I_n, moreover |D_n|=a_n/2. If you define B_n=-D_n (that is the each element in B_n is opposite to some number in D_n), then D_n is dense in (-n,-n+1) and |D_n|=a_n/2. If you den define [math]A=\bigcup\limits_{n=1}^\infty B_n\cup D_n [\math], then A is open dense and of measure m.
>>
File: 1585072263852.png (11 KB, 600x99)
11 KB
11 KB PNG
How to type it into Wolfram Alpha or change it to other form to get a result?
>>
>>12361779
Or a simple python/C++ code to calculate it?
>>
>>12361779
I got 8.68147e+155, is this correct?
>>
File: 1600464057764.png (4 KB, 199x135)
4 KB
4 KB PNG
>>12361814
>>12361837
>>
>>12361892
Thanks
>>
>>12361779
nigg isnt it just (5!)^3?
>>
>>12362011
No.
>>
>>12362011
n-no, I'm retarded
>>
(5!)^(1+5+25)
>>
File: 1593400159332.png (21 KB, 1273x332)
21 KB
21 KB PNG
is there an equal sign between these two or not?
>>
>>12362204
No. Operator precedence matters. You can't interchange the order you perform an addition and a multiplication and expect to get the same answer.
>>
>>12362217
Thanks
>>
How do I Physics? I think the math I need to do is pretty simple. I can also answer most of the conceptual questions at the end of the chapter correctly, but for some reason everything gets jumbled up when I actually try doing the real problems. If I know the math and I "get" the concepts, what exactly is my problem?

I have a feeling that maybe I'm just regurgitating what I read from the chapter when faced with the conceptual questions which is why I get them right, but I have no idea how to reach a higher level of comprehension.
>>
File: dsfdsfsdfsdf.png (66 KB, 751x325)
66 KB
66 KB PNG
Would it be correct to say that a spring does positive work is the displacement is towards the equilibrium position and negative if it is away from the equilibrium position?
>>
>>12362383
Physics is about setting up the right equations, plugging in values or computing equations is just math.
>>
Why do redditors like the "correlation does not imply causation" meme so much?
>>
File: DlpDqVKVsAAxd44.jpg (40 KB, 661x671)
40 KB
40 KB JPG
What exactly is a "synapse"?
Is it just the gap itself, the space between an axon terminal and a dendrite?
Or does it include the axon terminal and dendrite, making a sort of junction?
Wikipedia uses words like "structure", while simpler definitions sound like a synapse is just that space and nothing else. I'm confused.
>>
>>12362480
because once you learn something that a lot of people don't know, you get pleasure by sharing it with them and feeling superior. this is an easy concept to understand and share and one that young people (i.e. redditors) don't often intuitively know.
>>
>>12362465
no. first of all this paragraph is really poorly worded. is there more to it?
doing positive work -> increasing kinetic energy of the block
doing negative work -> decreasing kinetic energy of the block
basically the difference is whether or not the work done by the spring speeds the block up or slows it down. your description is technically what would happen, but it's really misleading to think of it that way.
>>
File: unknown.png (67 KB, 755x253)
67 KB
67 KB PNG
>>12362660
Here's the preceding paragraph.

I don't really understand what it's trying to say.
>>
>>12362738
it's just saying in a really roundabout way
[eqn] E_i= \frac{1}{2}kx_1^2 \\
E_f = \frac{1}{2}kx_2^2 \\
W=E_f-E_i [/eqn]
E is initial and final energy, W is work. In the absence of nonconservative forces, the work done on or by a system is equal to the change in energy (work-energy theorem). This can be positive or negative depending on whether the initial energy is lower or higher than the final energy.

Whatever book this is is shit.
>>
>>12362762
>>12362738
also, it's worth noting that this discussion has nothing to do with moving a block like I thought. it's just about stretching compressing a spring. there's no kinetic energy since you're assuming the stretch/compression is slow and controlled, you're just interested in the change in stored potential energy of the spring.
>>
>>12362762
Alright, thanks. That is a really roundabout way of saying it. I thought they were actually saying something new instead of just trying to put the formulas into words.

The book is Young and Freedman. I'm not really required to use this text. Can you recommend another?
>>
>>12362781
resnick if this is a calculus-based course. although I've heard good things about young and freedman so maybe this is just a shit passage.
>>
>>12350419
Does time for a person living at the equator flow slightly faster than for one living near one of the poles? Tangential speed at the equator is higher isn't it?
>>
File: potential.png (10 KB, 409x73)
10 KB
10 KB PNG
Please help me find my logic flaw here:

Initially I solved this by realizing that the kinetic energy of the bullet is equal to the potential energy of the combined masses at their peak of displacement. Let [math] m_1 [/math] be the mass of bullet and [math]m_2[/math] be the mass of the pendulum, let [math]v_1[/math] be the speed of the bullet before impact and lastly let [math] v_f[/math] denote the speed the pendulum moves at after impact.

So at it's peak, the potential energy is [math](m_1+m_2)g(0.12m) = 2.36J[/math]. So because energy is conserved, this potential energy is equal to the kinetic energy before impact [math] \frac{1}{2}(m_1)v_1^2 = 2.36J \rightarrow v_1 = 21.72m/s[/math].

But that's wrong and the right answer is ~308m/s. I know how to get the right answer, but don't see why my approach was wrong. The right answer employed the conservation of momentum:
[math]m_1v_1 = (m_1+m_2)v_2 \rightarrow v_1 = \frac{(m_1+m_2)v_2}{m_1}[/math]

Where [math]v_2[/math] is solved in the K.E=P.E equation above and found to be [math]1.53[/math]m/s. That approach also makes sense to me, but I still don't see why mine was wrong.
>>
Math friendos i have a question:
Lets say you have a list of n items and someone has chosen one at random. If i am to make lists of items and ask them if their item is on the list (so a guessing game) is the fastest method to just do a list withhalf their items, then if their item is on it repeat, halfing the list every time, or is there some crazy cool optimised way of figuring this out with less lists.

Idk math but i guess the smallest solution is number of lists is .5n + .25n + .125n ..., element tends to 1. Idk whats the proper way to write that E(n->1) .5n + .25n + .125n.. that seems slightly off
>>
>>12363172
So in other words we have 'the right away':
[math]
m_1v_1 = (m_1+m_2)v_2
[/math]
and
[math]K.E=P.E \rightarrow \frac{1}{2}(m_1+m_2)v_2^2 = (m_1+m_2)g*0.12 \rightarrow v_2 = 1.53m/s [/math]
plug v_2 into the first eqn and solve for v_1:
[math]
v_1 = \frac{(m_1+m_2)v_2}{m_1} = 307.53
[/math]

Then my wrong way:
[math]
K.E_{bullet} = P.E_{m_1+m_2} \\
\frac{1}{2}m_1v_1 = (m_1+m_2)9.8*0.12 \rightarrow = v_1 = \sqrt{\frac{2(m_1+m_2)9.8*0.12}{0.01}}
[/math]
>>
>>12362480
Because 4channelers love the "it's correlated therefore it's the cause" meme, so they go to war with each other over it
>>
>>12363172
> Initially I solved this by realizing that the kinetic energy of the bullet is equal to the potential energy of the combined masses at their peak of displacement.
This is incorrect. Energy is only conserved for an elastic collision. Any collision where the objects end up with the same velocity is inherently inelastic (the missing energy is accounted for by the deformation of the bullet). So you can't use conservation of energy here; you have to use conservation of momentum.
>>
>>12363479
>Any collision where the objects end up with the same velocity is inherently inelast
I was missing that key piece, thanks! These problems are fun.
>>
Definitely got a stupid question for you, /sci/.
I'm a cyclist. Normally I do strength training in a gym in the Fall/Winter in preparation for the following racing season, but gyms are all closed where I am so I can't do that.
I decided to do 'force' training on-bike as a substitute.
What I'd like to know, is how many pounds of force, on average, I'm delivering to the pedals.
I do 5 minute sets of 50-60rpm cadence at around 300 watts. I have a power meter (rear hub-based; PowerTap if you want to know), so I know it's about 300 watts, and I know the torque is more-or-less 10.5Nm on average. What I don't know how to calculate is how many pounds of force each leg is delivering to the *pedals*.
Basically I want to figure out what each leg, through each pedal stroke, would be 'lifting' if I was doing a weight-based exercise.
If you need more information I can probably provide it, but I think knowing cadence and torque at the rear wheel is enough -- but I may be wrong.
If no one wants to help that's fine, I'll be doing what I'm doing anyway, but it would be helpful to me to know what the equivalent would be in a weight-based leg exercise.
Thanks in advance if you decide to help.
>>
>>12363913
if your torque is 10.5Nm on average, you need to divide this by the length of your pedals (in meters) to the center of rotation to get your average force. then divide by two to get each leg's average force.
you can make it more accurate by approximating how much time you think you're pushing, but this should be a good order-of-magnitude
>>
>>12362607
That does make sense.
>>12363251
>4channelers love the "it's correlated therefore it's the cause"
We do?
>>
>>12364096
The use of 4channelers should have been enough to tell you hes a shitposter
>>
If a bunch of different pharmaceuticals haven't worked for me, should I try electo convulsive therapy? Or try taking St. John's Wort?
>>
>>12364101
For what? Major depression?
>>
>>12364114
I'm always tired, have terrible memory and concentration, fall asleep while driving. Tried so many things and the only thing that helped years ago was Wellbutrin for a few months, it hasn't worked on subsequent attempts.

Psychiatrist seemed like she's running out of ideas just like a number of other doctors and psychs have in the past. Really nervous about the next appointment. As a kid I was diagnosed with OCD, PTSD, generalized anxiety and social anxiety. I don't know if major depression might actually be the case.

I'm really losing hope I'll ever feel normal like I did when Wellbutrin worked. I was so productive and was turning my life back around so fast. But no matter how much I go to the gym, get plenty of sleep, no matter how well I eat, I always feel so fucking terrible. I fucking loved my life when Wellbutrin worked, every problem I ever had went away, I had tons of energy and everything I ever struggled with like math became so easy I enjoyed it. Was even learning Japanese on the side. I feel so fucking hopeless.
>>
Why are cows are docile but their fathers are violent? How did farmers figure this out?
>>
>>12364099
My brain honestly doesn't even register whether people are being serious or not, I just thought it was a good opening for someone to make a joke.
>>
>>12364128
Thats an interesting path of events. To put it blunty i think your psychiatrist may be hesitant to label you with major depression because its easy to latch on to a diagnosis and inevitably live a life as if depression is what you are. Anxiety and depression of course overlap, and theyre taught in a manner that unfortunately means theyre sometimes treated in the same way. To focus on the word treated for a second, thats where you shouls try and change your approach. We need to make sure you are trying to manage your diagnosis. Unfortunately i cant give you a management plan online, but youve certainly taken steps to try and manage it.

Its harder when youre on a typical day plan and diet like youve said, we often think they will make a large impact when we read about foods that increase gaba and whatnot and are dissappointed when they make no difference. In reality the claims of a lot of things are amplified beyond realistic expectations. So then what do we have to change? Simply saying our outlook doesnt help much. What do you think would needs to be adjusted?
Regardless, Ganbatte, watashi no tomodatchi.

Sidenote. Look into the way bupropion works if you havent, its an interesting drug. If you drink or smoke stopping may help, but it would be a delayed effect.
>>
>>12364089
Hmm, the result of that doesn't look right.
Since we're talking about a bicycle crankset, would the 'center of rotation' actually be the chainring and not the crank axle?
Also since the torque is being measured at the rear wheel hub and not at the cranks, would the gear ratio make a difference? Seems to me if I'm in 52:11 (most of it is) then I'd have to produce about 4.7 times more torque at the cranks, am I right?
>>
[math]\displaystyle \sum_{n=1}^\infty \frac{n^2}{n^3+1}[/math]
What test would I use to prove divergence?
>>
>>12364446
nvrmnd, limit comparison test
>>
>>12364128
Have you ever had a sleep study to check for something like apnea? Might be a dumb question but it can still present in people with average or low bmi, though less common.
>>
>>12364675
Back in 2015 I did and they found nothing. If I could get my current insurance to let me do it again I'd definitely try. Going to get my hormones tested again.. I did once and they found nothing off, but my mom is hypothyroid.
>>
I'm working through algebra by artin, but I'm a brainlet so I'm stuck on the third exercise.
How can [math]s(n) = n + 1[/math] have a right inverse since it's domain and range are {[math]{1,2,3,..}[/math]}
Also, 0 is not in the domain. For a left inverse, isn't it [math]{l}{s} = {Id}[/math]. The [math]Id[/math] for {[math]{1,2,3,..}[/math]} doesn't exist.
Even with an Identity, you would still need negative integers, which are not in the domain or range.
Can anyone give me a hint in the right direction?
>>
>>12364696
The best hint I can give you is that you need to reread most of this chapter because you have absolutely no idea what you're saying and most of this is gibberish. When you start claiming that f(n) = n doesn't exist you need to stop and re-orient yourself, because you're lost.

Real hint:
s can't have a right inverse because it's not surjective. There's no way to make s(r(1)) = 1 valid.
There are infinitely many left inverses for the same reason. Since s will never output 1, the equation l(s(n)) = n puts no restriction on what l(1) has to be, so l(1) can be any natural you like.
>>
>>12364696
> How can s(n)=n+1 have a right inverse
Read the question again.

> Even with an Identity, you would still need negative integers, which are not in the domain or range.
The form of a map is not restricted by the set, only the result matters, so why would it disallow the use of negative numbers?
>>
>>12364775
>doesn't disallow negative numbers
Oh.
>>12364751
>L(s(n)) = n
What I was trying to say was that that is impossible because the set does not contain negative numbers, but I just don't know what I'm talking about.
I was also thinking about Identity and inverses the wrong way.
When I read the definition for an inverse, I assumed it had to follow the equation
[math]ls=Id[/math] where [math]Id[/math] is the identity for the set
After thinking about it for a few seconds, I see why I wasn't making any sense.
All I needed to do was reverse s(n), not try to satisfy the above equation.
If I think about [math]n[/math] as the [math]Id[/math] for [math]s[/math] it does satisfy the equation.

Thanks for the help.
>>
[math]n! \sim \sqrt{2 \pi}n^{(n+\frac{1}{2})}e^{-n} [/math]

What's the point of "approximating" factorials with Stirling's formula? Seems like doing a bunch of whole number multiplications would be easier than doing exponentials, square root of pi, etc all that Stirling's formula sheit

Is recursion so much worse than actually having to do computations with transcendental numbers? Just seems weird to me
>>
File: unknown.png (98 KB, 1031x431)
98 KB
98 KB PNG
For part a, should m 1 have 0 final velocity? I'm kind of confused by the wording "just as m1 hits the table". I don't know if it means there's still velocity or if it already stopped.
>>
>>12364861
Because there may be time where you want an analytic solution using Stirling that you can't if is it left as a factorial. For example the differentiation or an integral of some function that involves a factorial.
>>
>>12364883
Ah, so the idea is it's like a more practical gamma function?
>>
A bullet of mass 0.0052kg is traveling at 672m/s when it goes through a block of wood of mass 0.7kg. When it emerges it's speed has been reduced to 428m/s.

I thought I'd solve this by finding the change in kinetic energy of the bullet during travel, 1/2m(v_i^2) - 1/2m(v_f^2), then assuming the kinetic energy that was missing from the bullet was transferred to the block of wood, so I'd solve for the woods new velocity, Delta K.E = 1/2mv^2

but the right way was to do mv initial for bullet = mv + mv_? for bullet after it's through the wood. Was my mistake assuming this was an elastic collision (like I did earlier)? It didn't initially strike me as inelastic, since it didn't mention 'friction' in the wood or anything.
>>
>>12350419
What are more formal textbooks for Feynman lessons? I am talking about all 3 volumes, general physics.
>>
>>12364861
>Is recursion so much worse than actually having to do computations with transcendental numbers?

Yes, also, in practice you replace those transcendental numbers with rational approximations.
>>
how would i solve y"-y'=x^-2 ,x>0
>>
how should I interpretate that some sequence is [math]n^{o(1)} [/math], where does it go to when [math]n \to \infty[/math]?
>>
>>12365306
if a_n is o(1), then a_n goes to 0 as n goes to infinity. In general, limit of n^{a_n} can be anything greater then 0 (it can also be 0 but I cannot come up whit an example from top of my head). For example, if a_n=1/n, then the limit is 1. If c>0 a_n= 1/(log_c(n)), then the limit is c, If a_n=1/(log n )^{1/2}, then the limit is infinity.
>>
>>12365277
Numerically.
>>
What does cos(x) look like on the Riemann sphere, in the neighborhood of infinity? It converges at 1, right? and sin(x) converges at 0?
So sin(+/-inf)=0, and cos(+/-inf) = 1.
What about ln(x)? or something like sinh(x), or arsinh(x)? Do the latter two form a natural step function out there?

Are there any respectable resources on this sort of stuff? I see there's an article about residues@infty, but what topic should I persue for more like this?
>please don't just say "undefined"
>>
>>12365749
It has a very, very bad singularity at infinity. Look up Picard's Great theorem for further info.
>Are there any respectable resources on this sort of stuff?
All meromorphic functions on the Riemann sphere are rational.
>>
So if I'm given the probability of a particle having h_/2 spin in y, how do i calculate the spin part of the wavefunction from that?
>>
>>12366431
by completeness you know the probability of spin down must be 1-(p spin up)
qm amplitudes are the square root of the probability, the problem here is you don't know the relative phase given just what you have. so you put in an arbitrary phase.

if you need the spin in the z basis just do a change of basis.
>>
>>12365238
landau
>>
>>12364871
no, because otherwise you'd be solving something different.
>just as it hits the table
that only means take the height of m1 to be 0.

when you do projectile problems and you want to solve when a falling object just hits the ground, you don't solve when its vertical velocity is 0 because that's at the top of its motion. you solve for when its height is 0.
>>
How can I predict how much the volume of a solvent solution will increase after adding a soluble substance?
For example, if I dissolve 100g of sugar in 100ml of water, what will be the resulting solution's volume?
>>
>>12350419

I've been hearing things about COVID inducing psychosis, lowering IQ, and causing permanent lung damage. Is there truth to these claims? As a 22yo healthy man what's the chance that happens to me if I catch it.
>>
>>12366707
This has been known in science for ages and it's not exclusive to covid. It happens with almost all infections. Number of suffered infections is directly correlated with lowered IQ in tons of studies.
>>
>>12366712
oh, interesting, is there any higher a probability for those weird permanent symptoms for COVID than for the common cold?
>>
>>12366723
It's possible but I'm not aware of any research on this.
>>
>>12366707
It's certainly true and such severe side effects are a lot more frequent than those the common cold can cause but the exact figures I'm not sure of. A simply google search will show thousands of people reporting insomnia, loss of taste, lethargy and so on months after they 'recovered' from covid.
>>
Sup, I dont want to disrupt thz thread with a fat ass post or anything but I have two questions regarding how to compensate lag in classes and cognition, I've asked them in here, thanks in advance to anyone who would be willing to answer
>>23142045
>>
>>12366791
You link to posts on other boards by doing >>>/pol/23142045
>>
>>12366804
Oh thanks a lot, I knew it was sorta possible but forgot how
>>>/adv/23142045
>>
it's been 2 years since HS and I barely remember anything I learned regarding math is there something I can use to refresh my memory or learn from the ground up?
>>
>>12366837
khan academy I guess
>>
>>12365238
What do you mean formal? There's the standard texts in first year physics, you could read something more advanced if you are up for the challenge like Taylor for Classical Mechanics, Griffiths for EM, Townsend for QM, Reif or Schroeder for Thermal Physics. The graduate level material is going to be well beyond your ken if you haven't done at least two years of university physics.
>>
>>12365749
If you want to know how f(x) behaves at infinity, look at how f(1/x) behaves at zero.
>>
>>12367321
>If you want to know how f(x) behaves at infinity, look at how f(1/x) behaves at zero.
I'm just gonna say that this is a great advice, for real functions as well
>>
>>12365359
Thank you. What if i'm told to prove some sequence is [math] n^{o(1)}[/math] ? I've tried taking logarithms and trying to put it in the form [math] o(1)\log(n)[/math], but I'm not sure if that's the best way to do it.
>>
File: unknown-7.png (25 KB, 754x144)
25 KB
25 KB PNG
i feel like i could easily solve this problem if i understood what a quarter-wave matching layer was. does it go on top of the water? whats its purpose?
>>
>>12368001
You are not wrong. If you were not taught what a quarter-wave system is and what it accomplishes during your course I can't see how you would be expected to know what to do otherwise.
>>
>>12368026
glad to have you on my side, anon
>>
>>12368001
probably another term for a quarter wave plate
made such that the light reflected off of the water won't propagate back outwards past the waveplate.

my guess is that this is a similar problem to anti-glare screens, that might offer some insight
>>
File: ellipse.png (3 KB, 267x338)
3 KB
3 KB PNG
we all know about calculating/measuring the circumference of an ellipse.

is it possible to do so without knowing the exact dimensions of the ellipse?
>>
>>12368039
we all know this? because it's highly non-trivial and it's not closed-form
>is it possible to do so without knowing the exact dimensions of the ellipse?
what does this mean? how do you calculate the circumference of a circle without knowing the dimensions of the circle? you need the radius to calculate anything
>>
>>12368047
well, ellipses are used in cryptography. therefore, there is a substantial difference between rendering an ellipse with dimensions beforehand and then calculating the circumference

but, what does 'closed-form' mean?
>>
File: 1593422679455.jpg (33 KB, 326x499)
33 KB
33 KB JPG
Any opinions on this? (from a science perspective) assuming it should be taken with a grain of salt
>>
>>12368052
closed-form, like there's an explicit equation for it. instead of having to evaluate an integral every time to solve for the circumference.

there is not a equation for the circumference of an ellipse. https://en.wikipedia.org/wiki/Ellipse#Circumference
>>
>>12368052
"In mathematics, a closed-form expression is a mathematical expression expressed using a finite number of standard operations."

and perfect circles are closed-form?
>>
>>12368058
Yes.
C=2pi*r
there is no similar equation for an ellipse
>>
>>12368052
> ellipses are used in cryptography.
you just proved you have no idea what you are talking about. elliptic curves have nothing to do with ellipses despite the naming similarities.
>>
File: ellipse2.png (2 KB, 352x262)
2 KB
2 KB PNG
growing eggs
>>
>>12368091
oh you're a schizo that explains it
>>
>>12368063
technically you need an infinite number of operations to calculate [math]\pi[/math]
>>
>>12368119
Technically, pi is just ln(-1)/i
>>
>>12368091
Lmao.
>>
File: unnamed.jpg (12 KB, 396x303)
12 KB
12 KB JPG
Someone was hueing too hard in my IP range, so I can't make a thread for this:

So if the universe expansion is not actually an expansion, but a change in this universal metric that dictates space, would it be sensible to abstract the universe as this magical snow globe full of matter that is slowly shrinking (the matter, not the snow globe)?

So if we regress in time, would that mean that prior to the Big Bang, every single particle and whatever there is out there was as big as the snow globe, but squished beyond imagination?

And if the universal metric is what causes the expansion, we can assume that space anywhere is expanding, so is that expansion taken in account when calculating atomic interactions? As, let's say that all the forces holding a proton and a neutron together can be summed up to be a certain theoretical xN. Do we have a constant eN between those two particles expanding the space, which would cause us to instead of measuring the xN attraction, to measure xN-eN?
>>
File: 1572475585568.png (27 KB, 207x243)
27 KB
27 KB PNG
>>12368409
>squished beyond imagination

funny, that's all that makes me think of
>>
if event 'a' has a 7% chance of occurring each time process 'b' is run, and b is run 3 times, event a occurring 3 times in a row has what % likely hood of occurring, 0.007% right?
>>
File: Net 2.png (36 KB, 1082x1016)
36 KB
36 KB PNG
I'm trying to make a cargo net without cutting my ropes

Anyone know what kind of pattern I should be using?

It's about a 11:7 ratio for length/width knot points with the rectangle around it.

Has this type of math already been solved somewhere? Just how to run one continuous line between a given array of points?

Like I'm trying to get as much symetry as possible, basically making an array of diamonds or squares inside the bigger rectangle.


My best attempt is rather uneven with the distribution.
>>
>>12368554
[math]0.07^3[/math]
>>
>>12368575
I think having the ropes move by 1 instead of 2 with each crossing should give more even hole sizes, at the cost of slightly less symmetry. Dunno if the problems been studied, I would guess probably not but who knows
>>
File: Net 3.png (48 KB, 1082x506)
48 KB
48 KB PNG
>>12368575
>>12368614
okay I have solved the cargo net problem I believe, how do I write a paper on this and get paid?
>>
>>12368575
Get a string and a paper, do some holes and do an experiment. My guess is that a square weaving is better than what is in your drawing. Like
__
| | |
| |__|

instead of

\ ^
\ / \
V \
>>
>>12368648
Convince a professor to help you. You'll also probably need to formulate and prove some theorems about your problem and solution.
>>
>>12368661
I made a thread for it

>>12368714
>>
File: IMG_1280.jpg (1.31 MB, 2200x2017)
1.31 MB
1.31 MB JPG
Mathematics. Explain how to determine the number of squares or the length on a roll of toilet paper by knowing the inside and outside diameter or nummer of revolutions on the roll. Really, I was thinking of printing press but, tp is more funny. I can't math. No bullying.
>>
what's a space time deflection?
>>
>>12369101
you just get the radius, and slice it into layers based on the perimeter.

Should be right
>>
>>12369101
Area of a circle is πr^2, area of an annulus (a circle with a hole in the middle) is πr2^2-πr1^2 = π(r2^2-r1^2). Divide by the thickness to get the length of the roll, divide that by the length of a sheet to get the number of sheets.

If the number of revolutions is n, the thickness is (r2-r1)/n, so length=π(r2^2-r1^2)/((r2-r1)/n) = nπ(r2+r1) = n*2π*(r2+r1)/2, i.e. the number of revolutions times the average length of one revolution.
>>
>>12367651
You want to show that [math] a_n \tilde{ } n^{o(1)}[/math]. If you have [math] a_n \tilde{ } n^{o(1)}[/math], then, by continuity of [math]\log x[/math], this is equivalent to [math]\log a_n \tilde{}o(1)\log n[/math], i.e. [math]\frac{\log a_n}{\log n}[/math]. So it suffices to show that [math]\lim\limits_{n\to\infty}\frac{\log a_n}{\log n}=0[/math].
>>
File: Untitled.png (35 KB, 447x164)
35 KB
35 KB PNG
how
do complex numbers not obey math?
>>
>>12369835
[math]\frac{1}{j}=-j[/math] is something that can be proven with math.
>>
>>12369838
wait youre right im retarded
>>
>>12369835
i*i*i*i = 1
i*i*i = -1*i = -i
[math]\frac{1}{-i}=\frac{i*i*i*i}{i*i*i} = i[/math]
yes imaginary numbers are weird
>>
>>12369835
What's j and what does it have to do with complex numbers?
>>
>>12350608
Anon I think I found your problem. You see, w̷̥̠̦̹̺͖͓̰͕̓̆̃̎̾͛ḩ̷͉̞̬̝͔̥̙̐͋̑̀̏̊͆̃̌͗͘͠a̸̖͖̼̗̋̃̂̚͠t̷̙̿̄͛̔͋ ̸̧̧̡̼̫͚͖͙͉̜̾y̸̛͚̹̠̻͉̪̪̾͜͝ȯ̸̪͈̝̜̮̒u̵͈͉̞̱͉̪̽̿̏͑͐̋ͅ ̵̡̭̥͔̣͕͉̘̀̆͂̒̌̕͜͜ͅh̸̘̯͖͓͚̼̓̽̈́̀͋̿̃̚͝͝͝ä̴̻̼͚̖̻̟̰́̐̀̑͂̇̂̊͒̾̋v̸̡̼̦̮͌̊̄̒̔̈́̐̊e̶̡͕̼̜̪̳͛̑́̉͘̕͜ͅ ̵̬̎͗̍́͆̒̌͝t̸͔̟̜̝̉̊̌͗̓̂͜ō̸͚̦͖͈̱̼̠̯̐́̀͠ ̷̢̫͎̤̟̝̯͓͎̼̄̃̌̐̉̃̀́̑͒͜͠ḍ̷̛͔̼͉̬́̐̈́̒̀̿̐̈̒̕̚ỏ̴̙̹̠̠͈͔̮̽͒͊̏̑́͒̀̀͝ ̷̡̤͍͔͉̿́͆́̎́̈́͊͌i̶̢̤̩̳̙͔͉̜̰̟̣̐͑̈́̂̓̃̀͂͋̒̚s̴̡̈́̓̈́̉̾̎́̕ ̷̹̘̜̪̜̣̭̪͓̺̾s̴̡̱̗̺͔̤̱͛͊̍͆́̒͝u̸̢̟̹̙̳̿̌̐̃̀̿͑̏̊͜b̵̧̡̡͎͚̬̮͇͕̣̮̑̇́̀͘t̶̩͔̗̣̜̑͊̓̐͛́̀͘r̶̪̼͓̳͒͛̍͊̏̍̌͘̕̚͝͝ͅa̸̟̮͚̮̍̀̍̓͌̈́̋͌c̵̞͉̙̜̼̻̪̝̓̃͂̊͑͗͒͌̈́̚t̷̠̍̌͗͛̈́́̂͑͆͌͘ ̴͍̙̻̒̍͒͛͝t̶̛̪͇̐̿̌̀̑̈́̉͝h̸͇̙̻̳̞͒̓̈́̄̈͋́̏̕̚͘e̸̹͕͑̓̀̍̾̀̈͋̓̌͌͒ ̷͚̖̺̤̀̈́̂̌͠d̴̝͉́̍̎̈́͐̎e̷͈̪̓n̶̡̳̜̱̤͗̂͜ő̵̯̋̌͂̐̀͛́m̶̨̢̻̻̻̥̫̖͑͒͑̿̌͛̚̚̚̕͜͠ì̵̻̇̈̇̐̇̎̂̚n̴͎̳͌̈̊͆̾͛͘͝á̶̢͙̯͔̮̘̤̳̪̪͗͒͛͂͝t̷̢̨̰̠̱̣͓͉͒͗́̈́̽̐̓̄̐́̕ọ̷̙̮͔̃̋͛͒r̴̛̯̓̒͆̍͛́͋̓͠ ̶̛̫̮̰͕̘͛͋f̵̧͇̞̹͙̯̞̩̹̗̰̓̑̒̏̔̂͝r̸̝̯̺͖̜̫̫̝̣̊͝ǫ̸̡̞̠̳̪͖͎̝̞͉̟̃̊̔̐̐͌̈́͛m̶̡̛̤͕͎̪̝͕̤͋̑͛́̍̚ ̷̪̬̟͒̎̈́͗̄͛͌̒t̸̬͚͉̙̺͕̯̤̰̗̂̒͂̿͝ȟ̵̨͉̟͕̤̬̞͊͋̀̊̀͠ͅe̶̡̳͈͉̣̤̞̟̼̤̺͊̾̔̒̌͌̈́͒̚͝͠ ̶̫̻̟̟̠̰͔̘̩̟͈̀̋̂͛͗͘͝͝ͅņ̴̫̙͈̯͔͎̘̘̆͛̔̽̕u̷̯̭̜͙̺̼͆̏̈́͐͆̈͗͋̏͌͋̿m̸̦̺̹̫̹̣̌̐̋̄͜e̶͇̣̜̰͆̆̄͑̀͐͌̈́͂͘ṛ̵͒̈́̑̓̏̉͝â̴̧͓̞̟̙̬̮̩͕̼͆̓̎͆͋̉t̸̨̢͕̯̪̝̦̳͓̋͐̇͌͋̋͑́̑͘͜͝o̴͖̼̺̯̗̒r̶͈̮͚̉͛̄̈́̓͋̂̔͘͝ ̸̹͑̿̈́̒̋͊͝ä̴̧̻́͐̃̃͂̊̕ņ̸̛͕̼̣̩̜̫̹́ḍ̵̭̪̹̱͌̂̆̈́ ̶͍͙̥͕̯̦̟̟̪̟̫̯̆͋̀͐̊̆̾̚t̵̛̤͕͋͑͗̀̐̚h̶̨̧̪͚̻̦͓͓͊͜ͅȇ̸̡̤͍͙̙̘͖̪̯̍͋̈́̃̉̎̚͜ń̵̛̯̤̯̼͇͚̠̫̄́͆͛̚͠ ̷̛̣̜̫̝̟͓̫̬̀̈́̔̇̿̊͂̈́͝t̶̨̥͎̟̳̓͐̽̎͆͂̽͂̀̐͜ͅŗ̸̨̠̜̪̻̦̄y̵͉̣̬̣̥̠̽͜ͅ ̴̹̺̦͂t̵̥̝̪̊̀̀̃̈͌̕̕u̸̮̯̥̩̥̠͉͂̍́̈́̈́̈́̎͑̃̈́̕͝r̴̠͔͖̙̬̜̭͓͇̥̎͂͂̀̿̄͂̑͜͝ņ̶̟̭̻̜̥̥͎̭̙̈̉̂̍̋͂̄̿͠i̶̼̖͍̯̥̒̈́̓́͆̄͊n̵̜͆̈́́g̶̡̧̻̝͚̣͍̎̏́͒̒͆͂̚͜ͅ ̷͙̭̟̬̱̦͈̀̈́̈́į̷͈̜̩̻͈̍̾̒̃̔͝ţ̸̨̖̳̝̰̉̃ ̸̧̟̙̰̤͔̳̜͆̉̍͑̐͘̚ō̵̧͈̰̪͉̓̔̌̎f̷͔̜̜̼̩̫͗͊̔̚f̸͍͎̱͍̱̮͂͛͗̀ͅ ̵͈͙̞͎̹̼̫̯͖̓͆a̷̳̘̮̜̩̻̬̘̞̜͒̇͂̇͌̉̕̚͘͜n̵̜̯̪̩͇͈̱̼̮͓̹͊͒d̴̜̗̠̜̼͌͆ͅ ̶̡̣͖̼̾̿͗̔̚ͅb̵̡͑̇͝ạ̷̧̨̱̮͍͚̦͓̥̺͛͂̑̈́̔̾͜͝c̸̖̜̳̥͚̹͚̣͒͊͋̄́͌̄̆̇̚͜͝ḵ̶̢̡̨̘̺̣̟̗̿͛͒̿͆̀̋̚͜͠͠ ̸̧̛͖̟̣͍͚͇͚̞̼̉̔̆̀̀̑̆̌̈́͝o̶̢̼͈̘̭͇͛̊̉͝n̸̡̟͙̱̬͊̈̈́̿̏͐̄͆̾̊͜ ̵̡͇̳͍͕͈̻͜͝a̷̺̼̜͌͂́̌̋͝g̸̛͓̫̜̝̼̞͑̀̑̓̓́̿̋̓̕͠ͅā̸̭͛͊̏̉͋̍̍͝͠ȋ̵̬̟̥̦̤̭͒̈n̵͖̟̳̪͇̳̖͉͙̰̫̠̓̇͊̔͝.̸̨̙̙̗̰̦̝͚̟̇
Make sense?
>>
File: Alu.jpg (20 KB, 444x253)
20 KB
20 KB JPG
Stupid question in regards to material science.

Let's say you have two aluminum rods, one is 2cm in diameter and the other 4cm diameter. You put them under identical stress conditions and identical atmospheric conditions. Would the 4cm rod last twice as long as the 2cm rod before it breaks due to corrosion and creep, or am i missing something?
>>
>>12369846
wtf?
>>
To whom it may concern:
I've recently switched 4G providers on my phone. Unfortunately, it turns out my new 4G's IP is range banned from making threads. Adding to this, my wi-fi has also been range banned for a good while now.
Someone take over making the threads, would you?
>>
>>12369843
Engineering typically uses j for the imaginary unit rather than i.
>>
>>12369890
Australia? Might try appeal though it seems the power that be takes a dim view on Australia and /sci/.
>>
>>12369928
>Australia?
Nope.
>appeal
Appealing a rangeban? You mean through feedback or by whining on IRC?
Pretty sure that doesn't do anything.
>>
How to find out if I have DID? Shouldn't the fact that I think it's a possibility make it so that it's certain I don't have it?
>there are some blank periods, it's normal to forget your childhood but I only remember certain things
>I'm not sure of the reason for the existence of certain things, namely writing only I could have done but I didn't do
>>
bumping my question >>12366620
>>
>>12369281
>>12369450
Thanks. I will try.
>>
>>12369504
Thank you, I'll try that.
>>
[math]\displaystyle \sum_{n=1}^\infty (-1)^n \frac{2n^2}{n^3+1} [/math]
How would I test this for convergence?
>>
>>12370721
alternating series criteria
>>
>>12370721
see if it is squeezed between two convergent series (squeeze theorem)
>>
>>12369977
Not sure how the appeal works, sorry.
>>
>>12370087
https://sciencing.com/calculate-spiral-6544041.html

OR
>>
>>12350419
Hi guys
Where can i find engineering journals?
I want to build a mini submarine
>>
>>12369890
It takes thirty seconds to make a new thread, come on lads, we're already at page 9.
>>
>>12371293
i would but my data is also b& from threads, and my wifi is perma-b& from posting in a cunny thread on /lit/
>>
>>12371304
>general dies because everyone's rangebanned and can't make new threads
Would be hilarious but sad.
>>
>>12371293
Worry not >>12371368
>>
>>12371371
Nice, thanks.
>>
>>12371271
Oh, thanks. Checking. I'm sure it will give birth to more questions.
>>
File: 1533178961438.jpg (52 KB, 600x448)
52 KB
52 KB JPG
Those of you who've worked in multiple countries, which ones have the best support for their scientists?
Which country is the holy grail for doing science?

I'll start
>Australia
>decent support while studying but shitty career prospects
>almost all science jobs are in the most expensive cities and even with a PhD they're not paying as well as some entry-level programmer with no work experience
>populace in general are pretty anti-intellectual so it's not well-regarded either



Delete Post: [File Only] Style:
[Disable Mobile View / Use Desktop Site]

[Enable Mobile View / Use Mobile Site]

All trademarks and copyrights on this page are owned by their respective parties. Images uploaded are the responsibility of the Poster. Comments are owned by the Poster.