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File: 1615853666585.jpg (257 KB, 750x842)
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Formerly >>13235012
>what is /sqt/ for?
Questions regarding math and science, plus related advice requests.
>where do I go for other questions and (advice) requests?
>>>/wsr/ >>>/g/sqt >>>/diy/sqt >>>/adv/ etc.
>how do I post math symbols (Latex)?
https://rentry.co/sci-latex-v1
>a plain google search didn't return anything, is there anything else I should try before asking the question here?
https://scholar.google.com/
>where can I look up if the question has already been asked here?
https://archived.moe/sci/
https://boards.fireden.net/sci/
>how do I optimize an image losslessly?
https://trimage.org/
https://pnggauntlet.com/

>where can I get:
>books?
https://spoon.wiki/Books
https://stitz-zeager.com/
https://openstax.org/
>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

>carreer advice?
https://sciencecareergeneral.neocities.org/
>help with calculus?
https://spoon.wiki/WolframAlpha
>charts?
https://imgur.com/a/pHfMGwE
https://imgur.com/a/ZZDVNk1
>tables, properties and material selection?
https://www.engineeringtoolbox.com/
http://www.matweb.com/

General advice for asking questions here:
>attach an image (animal images are best. Grab them from >>>/an/)
>avoid replying to yourself
>ask anonymously
>remember to check the Latex with the Tex button on the posting box
>if someone replies to your question with a shitpost, ignore it
>avoid arguing with Yukarifag
>do not tell us you came from whatever the fuck board, /pol/ in particular
>do not mention how [other place] didn't answer your question so you're reposting it here
>>
>>13260744
Yeah retard
>>
In tossing
a fair die, let A = {2, 4, 6} and let B = {1, 2, 3, 4}.
P(AB) = 2/6 <<<<<why is this so?
= P(A)P(B) = (1/2) × (2/3) <<<why are these the values of P(A) and P(B) respectively?
>>
>>13260775
why?
>Witten so smart
> Witten is a woke liberal
> Witten must be right and I'm wrong
is this your thought process?
>>
>>13260779
intersection is AB = {2,4}
P(AB)=P(A)P(B)=2/3 * 2/4 = 2/3 * 1/2
>>
>>13260779
[math]
P(A U B)=P(A)+P(B)-P(AB)
P(AB)=P(A)+P(B)-P(A U B)=3/6+4/6-5/6=2/6=1/3
[/math]
>>
>>13260831
Thanks
>>
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What the hell does this mean?
>>
>>13260919
absolute value
>>
>>13260699
What are the 0s of the Riemann zeta function?
>>
>>13260923
Thanks.
>>
>>13260919
this post should be used as OP image for this thread
>>
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>>13260699

can someone explain to me what happened to
-c1x and c1 in second and third equation?
>>
>have master's
>thinking about applying to doctoral programs in the fall
>have little-to-no research experience
I hear you need a lot to get into a doctorate program but lolidk anything. Any advice or experiences overall? I'm sure the universities I'd apply to would be important as well in terms of accepting my subpar ass.
>>
>>13260474
once you have general bio under your belt, you can go in any number of directions. personally, i felt like cells were the most important thing to know about bio, so i grabbed a copy of Alberts' Molecular Biology of the Cell and read bits of that. it has really nice illustrations, if nothing else
>>
The latex site thing in the OP is down, how do I post things like the integral symbol?

I have a basic integral question:
f(x) = x^3 + 2x^2 - 3x
An interval is given, I = [-2;2] for example, and the graph has the zero points -3, 0 and 1. I'm supposed to calculate the area between the x axis and the graph. In that case I just use -2 for the lower and 2 for the upper integral limit, right? Which results in 10.67 in my calculator. But on the graph I see that the area between 0 and 2 is below the x-axis, yet the area gives a positive result (3.33). Why is that? And are the zero points just irrelevant if I just have to enter the given interval into the integral anyways? The exercise wanted me to calculate them, so I'm unsure.
>>
>>13261326
PhD isn't worth it.
>>
>>13261862
If you're rich that is. If you're poor it's definitely worth it.
>>
>>13261879
it's the other way around
>>
>>13261883
Nope. If you're poor it's an easy way to get money. If you're rich you can get a much better job through connection or nepotism.
>>
>>13261896
If you're poor, it's an easy way to waste your 20s working for mcjobs tier pay with no real benefit at the end.

If you're rich, you never worried about money anyway and probably just wanted another status symbol.
>>
PhDs are reserved for upper middle class academic families. People who do them coming from the outside are fucking retarded and never get hired for obvious reasons.
>>
Let [math] H [/math] be a subset of [math]G[/math] such that [math]H = {g^5 | g \in G}[/math].

>Prove H is a subgroup of G
Because [math]G[/math] is a closed group, we have [/math]a^{-4}, b^{-6} \in G \rightarrow a^{-4}b^{-6} \in G[/math]. Then in [math]H[/math] we must have [math](a^{-4}b^{-6})^5 \rightarrow ab^{-1} \in H[/math]. By the subgroup test, this shows what we set out to prove.

Good?
>>
>>13261793
> graph has the zero points -3, 0 and 1.
> But on the graph I see that the area between 0 and 2 is below the x-axis
The interval [0:1] is negative, and the integral over that interval is -7/12. The interval [1:2] is positive with integral 47/12. The integral over [0:2] is 47/12-7/12=40/12=10/3.

The sign of a polynomial usually changes at each root (if it's a repeated root, the sign changes if the root is repeated an odd number of times but not if it's repeated an even number of times).
f(x) = x^3+2x^2-3x = (x-1)*x*(x+3)
For x<-3, all three factors are negative and f(x) is negative.
For -3<x<0, (x-1) and x are negative, (x+3) is positive, and f(x) is positive.
For 0<x<1, (x-1) is negative, x and (x+3) are positive, and f(x) is negative.
For 1<x, all three factors are positive and f(x) is positive.
>>
>>13261936
Wrong. Universities are fair when hiring people.
>>
>>13260807
Witten's an old boomer that still trusts establishment media. He thought kyle rittenhouse was a white supremacist trying going to shoot protestors.
>>
Why have I lost all motivation for programming? When I first started learning it back in high school I could sit down for hours hashing out an algorithm to do whatever, but now automating even the simplest task feels like a huge chore. I can still find motivation to do other things, just not programming.

t. not a CSlet
>>
>>13262266
>. He thought kyle rittenhouse was a white supremacist trying going to shoot protestors.
source?
>>
>>13262122
>The interval [0:1] is negative
Oh, I misread the graph. That suddenly makes a lot more sense.

>f(x) = x^3+2x^2-3x = (x-1)*x*(x+3)
I kinda got lost on this and the following steps. What exactly are we doing here, rewriting the function so it's easier to see the zero points? I don't really get why we're looking at the factors one by one or what each one affects exactly. If f(x) as a whole is negative for x<-3, and positive for -3<x<0, then we know that entire integral is positive, right? And when it then goes from that positive to negative in 0<x<1, it's negative. Is that the idea?
>>
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I remember hearing a term that describes a situation where someone gets so engrossed in something that they miss the big picture.

Like they spend so much time analyzing some tertiary detail that they dont realize that the results dont match the theory, and they continue on down the wrong path because of it

anyone know what I'm talking about? (its not "pathological science" btw)
>>
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>>13262377
>>
>>13262390
yeah, but I'm pretty sure theres a term that wraps that idea up in one or two words
>>
>>13262403
>>13262390
thanks for the reply, btw
>>
>>13262377
>a term that describes a situation where someone gets so engrossed in something that they miss the big picture.
missing the forest for the trees?
>>
>>13262452
>missing the forest for the trees?
never heard that one, but it does describe what I'm thinking of
>>
>>13262403
tunnel vision? idk that seems worse than the forest for trees one
>>
>>13262377
Tunnel vision?
>>
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how to prove closure for [math]a * b = ab-3a-3b+12 \in R\{3\}[/math]? i couldn't get my backslash to show but it's the reals but not 3. i've proved associativty, identity and inverse already
>>
>>13262403
Sunk cost?
>>
>>13262582
>couldn't get my backslash to show
It's \setminus
Have you proven that the result of the operation is never 3? You only really need to compare equivalence classes mod 3. This would be valid for integers, but you can extend it to reals by arguing that if a and b are not integers, then the result is not an integer.
>>
>>13262582
> a * b = ab-3a-3b+12
= (a-3)(b-3)+3
a * b = 3
=> (a-3)(b-3)+3 = 3
=> (a-3)(b-3)=0
=> a=3 or b=3
If neither a nor b can be equal to 3, then nor can a*b.
>>
>>13260699
>>
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>Early Transcendentals Calculus textbooks
>Late Transcendentals Calculus textbooks
which is better? why should I choose one over the other?
>>
What is the difference between "Let" and "Assume"? Also what does it mean when textbooks say "necessary" or "sufficient"? t. ESL
>>
>>13262745
If your uni requires you to use Stewart, might as well use Khanacademy anon. It's pretty much the same thing.
>>
>>13262697
d'oof! my factoring didn't work so i didn't think it was that easy, thanks anon
>>
>>13262747
"let" and "assume" mean the same thing

"necessary" means you must ______ something
"sufficient" mean you can or may _______ something
>>
I don't really get this question: Show [math]x \in G [/math] commutes with all elements of group [math]G[/math] iff [math] [x] = \{x\}[/math], where [math]\{x\}[/math] is the equivalence class containing [math]x[/math].

The equivalence class of [math]x[/math] is the one element set, [math]{x}[/math]? And I'm supposed to show that this means it commutes with all elements in [math]G[/math]?
>>
>where {x} is the equivalence class containing x.
*where [x] is the equivalence class containing x
>>
>>13261896
>>13261930
lol i'm 31, a poorfag, and can't find shit in my city or nearby with my degree. it's more of a "what else am i going to do with my life?" question at this point. i don't want to teach though but i'd like to get a doctorate and do something with that, ideally working with animals
>>
>>13262890
You didn't specify what the notation means but it looks like your equivalence relation is the conjugacy classes, and it's asking you to show that if the conjugacy class of x is just x then x commutes with everything in the group
>>
>>13261326
The answer to this depends heavily on what you want a PhD in. Minimal research experience matters very little for something like a math/stats PhD. If you're trying to apply to a lab science like chemistry, no research experience at that level is essentially fucked.
>>
>>13262986
>it looks like your equivalence relation is the conjugacy classe
how the did you deduce this? it's correct btw, the previous was about conjugates.

>it's asking you to show that if the conjugacy class of x is just x then x commutes with everything in the group
if the conjugacy class of x is just x then is x the identity?
>>
>>13261793
>The latex site thing in the OP is down
It's up now.
>>13263005
>The latex site thing in the OP is down
No, it's just mapped to itself by every conjugation.
>>
which symbol is preferred for frequency: "v" or "f"?
>>
i just flunked analysis, what do i do now?
>>
>>13263005
>how the did you deduce this?
conjugacy classes are extremely common and they're the only equivalence relation that would make any sense here

>if the conjugacy class of x is just x then is x the identity?
no, not at all.

When you do these kinds of algebra problems most of the problem is just carefully writing out what you've been told in symbols.
You know that the conjugacy class of x is equal to {x}. Write down the symbolic definition of the conjugacy class of x. Then see what you can do by knowing that every element of that set is x.
>>
>>13262697
does this prove closure?
>>
>>13263027
retake it next semester and don't fail this time
or become an hero

your choice really
>>
>>13263031
>Write down the symbolic definition of the conjugacy class of x
So, for [math]g \in G[/math], the conjugacy class of x is [math][x] = gxg^{-1} = {x}[/math]? Or was that wrong?
>>
ah crap meant to say
[math]
= \{x\}
[/math]

always forget to backslash my brackets
>>
what letter should I use to denote imaginary numbers when I already used i and j for indices?
>>
>>13263027
Take algebra instead
>>
>>13263027
what did u learn
>>
>>13263053
penis
>>
>>13263049
Basically yes, but you should specify that the conjugacy class is not one particular gxg^{-1}, but the set of all gxg^{-1} for every g in the group.
And that's essentially the entire problem because you've written down that gxg^{-1} = x for all g, and your goal is to prove that gx = xg for all g.
>>
>>13263037
i unironically wanna kill myself right now.
>>13263054
already did it.
>>13263061
up to continuous functions i guess
>>
>>13263053
Use m and n for indices

>>13263049
The conjugacy class of x will only include x if it commutes with g and its inverse. This is easiest to see if x is the identity.
>>
>>13263053
either be one of those gigantic faggots who just uses [math]\sqrt{-1}[/math] everywhere or switch your i index to a k
>>
>>13263067
what would u do differently
>>
>>13263066
i hate that i can have the solution right in front of me but still not get it all. I liked learning algebra on my own when I'm squeezed on time it makes me want to blow my brains out like nothing else.
>>
>>13263067
>i unironically wanna kill myself right now.
here, watch this, it'll help
https://www.youtube.com/watch?v=Bn2jEXqLcSQ
>>
>>13263068
>conjugacy class of x will only include x if it commutes with g and its inverse
because [math] gxg^{-1} = gg^{-1}x = x[/math]?
>>
>>13263078
everything, but it's easy to write words, i don't know if i'll have the strenght to keep going
>>
>>13263111
oh come on ya little poop, don't be so melodramatic. there's more to life and if you retake it's behind you
>>
>>13263053
there is no scenario where the two would collide
just keep your namespaces separate mentally and carry on
>>
>>13263107
Yes.

>>13263124
What about Hermitian matrices?
>>
>>13263116
i'm on my 4th year already though and i still didn't do analysis, that's what makes me depressed
>>
>>13263138
do you have an imaginary number of dimensions to keep track of?
>>
>>13263138
>>13263150
alternatively, there's [math]i[/math] and then there's [math]\mathrm i[/math]
>>
>>13263140
why do you care so much? did u think u were gonna be a phd genius or something?
>>
>>13263212
not a genius, but also not this pathetic.
>>
What happens in a semiconductor laser with a certain gap energy when I insert, from the outside, a photon with a frequency such that
h*f != gap energy ?
Do I still have some kind of emission?
>>
>>13263161
I considered that, but that's even more confusing
>>
>>13263138
>>13263066
So is this a sufficient proof to the question of
>Prove x in G commutes with all elements of G iff [x] = {x}, where [x] is the equivalency class containing x
If the conjugacy class [x] = \{x\}, then we have (for arbitrary g in G)
[math]
[x] = gxg^{-1} = \{x\} \rightarrow gxg^{-1} = x \rightarrow

gxg^{-1} = gg^{-1}x = xgg^{-1}
[/math]

So x commutes with all elements of G iff [x] = {x}
>>
Anywhere that explains top, lin and Cr homeomorfisms in a simple way? Took an ODE optional class without knowing it'd be heavy in the theoretical math side (physicsfag) and kinda lost in this aspect, this is a class that is obligatory for mathfags and teacher is assuming everyone knows this shit.
>>
I switched from med to biomedical engineering and after four years without any maths have an intro to numerical analysis. Things like ODE, PDE (never taken a differential equations class), newton's method, Banach theorem.

I'm smart and I understand these things but I severely underestimated the time it takes to learn this. I gave myself 2,5 days for this whole course (starting from zero) a nd have exam tomorrow and will fail hard. I hate studying proofs, after I understanding the proof I don't want to be able to reproduce them. I'm not smart enough to just reproduce them with just comprehending them, I need to study them more or less by heart. rant over
>>
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An oldie, but a goodie. Last question before I lay on a hammock all summer. I have no goddamn clue how to read these runes, but I'm going to reread the relevant definitions and bang my head against the wall until I figure it out by midnight hopefully.
>>
>>13263324
What runes, it's just Lagrange notation for differentials.
>>13263263
>top, lin and Cr
Topological, Piecewise linear and [math]C^r[/math]?
The distinction really isn't easy to visualize in any meaningful way. Just look at the definitions. Topological only takes into account topological data, pl considers pl-data and C^r establishes compatibility between differentials.
>>
>>13263334
>runes
it was the wrong image lol
>>
>>13263234
well, ur attitude is about as bad as it can right now desu. if you can believe it's no big deal, it won't be. good luck on whatever u do, and if u want to help a scrub out: >>13263328
>>
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>>13260699
How do you read math if you don't know what any of the letters are?

I spent two hours yesterday trying to figure out what the fuck an [math]\textit{e}[/math] was standing for only to find that it's a mathematical constant.
>>
>>13263355
there's no point in life anymore, i'll never get accepted for a phd like this, it's pretty much over for me, i wanna kill myself, my life is pure pain. sorry, but i'm gonna leave now to cry in in my blanket.
>>
>>13263477
phds are gay anyway, if you failed analysis u need to accept ur not cut out for it. just learn2code and get a comfy job instead, but only after providing me a complete and detailed answer to my question with proper typesetting
>>
>>13263482
that's why i'm depressed dumbass, i'm not gonna accept that ever. i wanted to do a phd so badly, it didn't even have to be in a prestigious place, i just wanted to prove that i could get one, but now it's probably near impossible, i'm complete trash for wasting all those years and all those chances.
>>
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Why do I like this random youtube comment so much?
>>13263328
>I'm going to reread the relevant definitions and bang my head against the wall until I figure it out by midnight hopefully.
Sounds like a solid plan.
>>
>>13263418
How do you read any language without knowing its alphabet?
>>
When and why is silver used as a gas?
>>
So I bought a book about nuclear & alternative energy but It's from 2006, should I still give it a read or is it too outdated?
>>
>>13263538
how do you know what's part of the "alphabet" and what are just situation-specific variables?
>>
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A ball is dropped from the top of a building and stops when it reaches the ground. Instants later a boy picks up the ball, raise it to the top of his head with constant vertical speed and throws it vertically. Ignore air resistance. What is the graph that represents the movement of the ball (displacement x time)?

Pic related is the first one.
>>
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>>13263585
And this is the second one. Please answer me fast. Thanks!
>>
>>13263572
You discern meaning from context clues, same as always
>>
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Does any anon here know any math word problems book in 日本語? I'm too dumb to understand literature, might as well do math while doing my reps
>>
>>13263585
This one.
>>
>>13263585
first one
>>
>>13263551
https://en.wikipedia.org/wiki/Vacuum_deposition
>>
Is there multivariable equivalent of increasing/decreasing function?
>>
Why is current (amperes) a fundamental si unit instead of charge (coulombs)?
>>
>>13263594
how do you find context clues in this case
>>
>>13263643
Beats me. I still think it's strange that they redefined the fundamental charge as a given number of coulombs, yet derive amperes (supposedly fundamental) from it and the second. I get that amperes being "fundamental" is historical, but you'd think they'd have called coulombs fundamental if they're now proportional to a natural constant
>>
what is Z/4Z
>>
>>13263679
The same way as you would if you were a first grader. Consult another source if you're confused by the what something means

>>13263692
Integers mod 4
>>
>>13263700
>mod 4
thats what i thought, what aboutb ZxZ/(4Zx6Z)?
>>
>>13263708
Z x Z is pairs of integers.
4Z x 6Z is all pairs of integers where the first is a multiple of 4 and the second is a multiple of 6.
(Z x Z) / (4Z x 6Z) is the equivalence classes of pairs of integers under 4Z x 6Z
>>
>>13263643
because it's way easier to measure 1 Amp (due to precision in voltage and resistances) and 1 second (thanks to atoms) than it is to measure a coulomb's worth of electrons

it's why they redefined mass, too. it's easier to get a precise measurement when dealing with things that can be controlled well (light) than just having an arbitrary mass of 1 kg floating around the world
>>
>>13263236
depends. if you're greater than the gap energy then yes, you'll still get emissions because you can excite the electron into the conduction band. if you're less than the gap energy then no, the material will just absorb the photon and get heated up
>>
>>13263721
im going to kms
>>
>>13263757
Weren't you telling the other lad not to kill himself twenty posts ago?
>>
>>13263783
yes but he was more serious
>>
I get what ZxZ/(4Zx6Z) is though, I think. I'd expect it's like:
{(4Z, 6Z), (1+4Z, 1+6Z), ....} for all unique pairs.

but someone else told me it's {4Zx6Z, (0,1) + 4Zx6Z, (0,2) + 4Zx6Z, ... , (1,0) + 4Zx6Z, (1,1) + 4Zx6Z)}. is this one right?
>>
>>13263806
More like the latter, yes
>>
>>13263815
how does the latter one make any sense? why does it go (0,1), (0,2)...(1,0),(1,1) - I would expect these pairs to go up to something like (4,6), for example.

anyway, so I'm trying to prove this latter thing that I don't understand yet is isomorhpic to {0,1,2,3}x{0,1,2,3,4,5}. i have a few tricks up my sleeve if i can figure out how to show that
>there's a surjecrtive homomorphism from ZxZ to Z/4ZxZ/6Z with kernel 4Zx6Z
>>
>>13263733
>>13263684
thanks
>>
i'll kill myself but i'm not gonna go down alone, i'll take that fucking teacher with me, he destroyed my phd dream
>>
>>13263843
There doesn't need to be a particular order, it just needs to hit all pairs up to (3, 5). Then you can disregard the (+ 4Z x 6Z) as your isomorphism
The way you wrote it before is alright, but I take issue with putting 4Z and 6Z in the tuple itself. I feel like it's taking a little too many steps at a time, and looks too conveniently close to what you want as a solution.
>>
>>13263869
well you seem to think I'm close to solving it, so that's good.. but I'm a lot farther away from solving than you think. I still have no clue what I'm doing, I at least now know what ZxZ/(4Zx6Z) and (Z/4Z)x(Z/6Z) mean though. And I think if I can prove that there is a surjective homomorphism from ZxZ to Z/4ZxZ/6Z with kernel 4Zx6Z, then I can use the fundemental homomorphism theorem and the first isomorphism theorem to show it's isomorphic.

but that's all just words and I have no idea how to really get there or prove it. I don't really get how ZxZ is homomorphic to Z/4ZxZ/6Z either since homomorphism means f(xy) = f(x)f(y) and i don't know how to interpret that here
>>
ok, WHAT IF i just rearranged the parenthesis? is that cool?

ZxZ/(4Zx6Z) = (Z/4Z)x(Z/6Z)
>>
>>13263955
Dude just fucking map [math](m, n) + (4 \mathbb{Z}, 6 \mathbb{Z}) \in \mathbb{Z}^2 / (\mathbb{4Z} \times \mathbb{6Z})[/math] to [math](m + \mathbb{4Z}, n + \mathbb{6Z})[/math], it's not a fucking hard proof.
>>
>>13264013
i just got to the same point, im getting so close bruther i can't wait to be done
>>
>>13260699
> Wittens head is to big to fit his profile picture
i am in awe
>>
>>13264013
stuck trying to show the mapping is bijective and homomorphic.
>>
>>13262745
Most uni's use early transcendentals because you need to use and know about those functions in other classes. But technically it is a less rigorous way to do calc.
>>
This is my last /sqt/ post for at least 6 months, sorry for shitting it up the past few days and thanks for the help. I fell way too far behind this term and have been barely skating by. I made a thread on /wsr/ trying to finish up this one:>>13264013
>>>/wsr/1040275
>>
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>>13260699
>see Ed Witten himself is on twitter
>this'll be interesting, I wonder what he -
>he's a woke faggot
EVERY FUCKING TIME
>>
>>13264545
what does it say about society that most of the smartest people hold similar political beliefs
>>
>>13264928
You mean how 99% of all humans up to this point would be considered right wing extremists by today's standards?
What it says is that not even the smartest person is immune to social pressure.
>>
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Medfags: Yesterday I for probably like the first time in my life I experienced significant visual distortions. Suddenly, in my field of vision, significant swirls appeared, unrelated to whatever was actually in the field of vision. Like a weaker form of AI deep dream images. I had 2 such episodes. I felt a bit lightheaded during them.
Notable: I had finals this week, and I have slept maybe totally 6 hours over the preceding 3 days (fueled by amphetamine, but I have done it often and never experienced this before).
I am not concerned, but what in the hell could this have been?
>>
>>13264931
Filtered
>>
>>13264255
Thank you.
>>
>>13264928
It shows that the intellectual extreme tends toward the irrational and the absurd.
>>
hello lads, i want to make pretty pictures, but to make those pictures it's helpful to be able to implement papers written by smart math folk.

if you were trying to shortcut your way into implementing said papers while understanding as little of the underlying math as possible, how would u approach it.
>>
>>13262218
reported
>>
>>13260699
Can anybody link me the channel/website of that gay asian math guy with an intense raceplay fetish?

People think I'm making it up.
>>
>>13262377
myopic
>>
>>13263026
ffffffffffffffffffffffffffffffffffffffffffffff
unless its normalized...
>>
>>13265163
Guy was a mathematician that dressed up in drag a lot and talked about how him and other asians are destined to be fucked by whites.

I would prefer to be less descriptive desu.
>>
>>13260803
>>13264545
Does anyone still have the old extreme right wing Witten memes?
>>
If you could choose, what vaccine or type of vaccine would you go for?

https://www.healthcareitnews.com/news/emea/four-types-covid-19-vaccine-snapshot
>>
>>13263742
Thanks. I'm assuming the emission is still gonna be of a photon with energy equal to gap energy, but what about its motion value?
>>
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when food goes in the mouth, it smells good, but when it comes out my anus, it smells bad.
why?
Please don't say bacteria.
If you do, why do the bacteria smell bad to us?
My dog likes to eat poo.
MY 3 yr old sister likes to eat poo.
Is it taught?
>>
>>13265558
>theonemirror reflectsitsself
oops
i namefaggoted wrongly, as i was thinking of poo while i was typing! ༼ ºل͟º ༽
>>
>>13264928
It shows that mathematical ability doesn't necessarily equate to actual intelligence.
>>
>>13265558
>>13265573
bad bot
>>
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>>13260699
how can i reduce the filesize further?
>>
>>13265884
You need a quantum computer.
>>
>>13260699
Chuds on suicide watch
>>
Where can I get the knowledge to build a house from scratch all by myself?
>>
>>13266065
this is an important topic, i need qualified advisors
>>
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What's the real relationship between the remainder of a polynomial division and its roots?

I solved a problem that was like
the remainder of ((x^2 + x - 1)^60 + (x - 2)^30) / (x - 1), which is 2 as you can simply put 1 that's the root of (x - 1) in the first polynomial and would become 2

But what if the second polynomial were from a higher order like (x - 1)(x + 1)? Its roots are 1 and -1, the remainders would be 2 and 0 if divided separately, could its remainder using that technique?

Also, what if the remainder is something like 5x + 3? Its also doable?
>>
>>13266355
Could I find the remainder from its division using that technique?*
>>
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>>13266355
Actually, the remainder of its division by (x + 1) is far from 0, P(-1) is that massive number, but P its divisible by (x - 1)(x + 1) so I'm even more confused now
>>
>>13260807
>I'm a woke liberal too
May I ask what made you retarded? Or were you always this way?
>>
>>13266483
>born retarded
Gotcha, that makes sense.
>>
>>13266489
:)
>>
>>13262275
hedonic adaptation. It no longer triggers your dopamine system
>>
What's the best resource for getting help as a premed? The /med/ thread is full of schizos
>>
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>>13266483
I see, I found a problem that were similar, and by seeing a solution I realized I could do it like:

P(x) = (x - 1)(x + 1)Q(x) + ax + b

For x = 1, a + b = 2
For x = -1, -a + b = 205891132094605

Which by solving it, results in ax+b being this monstrosity of remainder I didn't see on the first time

I think this is true for all polynomials, you can find the remainder of P/(A*B*C...) if you know the remainder of P/A, P/B, P/C....
>>
Is an online master's in nuclear engineering from Purdue or Penn State worthwhile?
>>
>>13266483
>I've always had weird beliefs but this is not the thread to go into that.
This is a containment thread.
>>
Hello anons :). What exactly does 'shift x and y according to dy/dx mean'? I have not taken calculus yet - but its popped up in my projects source code so might as well try.
>>
>>13267627
I'd assume it means to extrapolate a value based on the derivative (the rate of a very small change). For example, velocity is the derivative of position, so if every loop you add a scalar multiple of the current velocity to the position of something, then the object will "move" with the velocity specified.
But it's a little weird since dy/dx would be an implicit derivative in this case. What's it used for?
>>
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>>13260699
>>13260937
Done.
>>
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[math]X[/math] is any metric space; define Cauchy sequences in [math]X[/math] to be equivalent if [math]\lim\limits_{n\to \infty}d(p_n,q_n)=0[/math], and let [math]X^*[/math] be the set of obtained equivalence classes. Show that [math]X^*[/math] with the metric [math]\Delta (P,Q)=\lim\limits_{n\to \infty}d(p_n,q_n)[/math] is complete.
Would it best to approach this by construction (like [math](p_n)[/math] in the limit of arbitrary Cauchy [math](P_n)[/math]), a topological interpretation, or somehow deducing it from [math]d:X\to R^{+}[/math]?
>>
>>13267802
The best way to approach it is to assume some random Cauchy sequence [math]P_j[/math] of Cauchy sequences [math]p_i[/math], replace all of them by sequences that are 'Cauchier', and then construct a limit sequence from those.
>>
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>>13260699
Has anyone here had hypnopompic (occurring after waking) hallucinations of spider/insect-like black dots (sort of like noise) moving/"crawling" on walls? Further, do yours self assemble into spiral shapes and can you will it to self order and return to a chaotic state? Also has anyone noticed that if in a state where your susceptible to these hallucinations and if you are in a room with little light and a spatially complex environment your brain interprets and animates the objects? eg a shelf with trophies and a lamp morphing into a sentry gun which points at you. Also I'm not schizo or anything I have a strong sense of reality. I'm just curious to see how common this experience is and see other people's stories since I find it interesting.
>>
>>13267837
Ohhh that's right, I can just use subsequences of [math](P_n)[/math] as nice as I want, thank you.
>>
>>13260699
Where can I go to pay someone to complete a math exam for me?
>>
>>13268271
>>
>>13268279
>>
>>13267902
This is basically what 80% of „HPPD“ cases are (although it’s not HPPD, if it’s not causing distress).
You are now basically seeing how much shit your brain otherwise filters out.
I used to have this as a kid and had it again now for about a year after taking too many hallucinogens but it’s faded again. It doesn’t matter because you won’t get any data for study out of it and it doesn’t change how you orient yourself in physical reality. Is kinda neat too look at but that’s it.
>>
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why do i have to "formally prove" that two manifolds are diffeomorphic
i just see them in my head and feel it in my bones, ya know?
>>
>>13266101
You got me on this one bunker tranny
>>
>>13260699
anyone know a good starting point for calculating the time it takes for a room's temperature to equilibriate assuming you open a window with a temperature difference
>>
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>>13266101
>>13266106
https://en.wikipedia.org/wiki/Oswald_Teichm%C3%BCller
>>
How do you implement neumann boundary conditions for wide finite difference stencils?
For compact stencils, you can just use ghost nodes and f[0] - f[-1] = df/dx, but for higher order stencils there are too many unknowns to determine the values at the ghost nodes.
>>
About climate change: If the local climate can differ from global average temperature, does a global warming necessarily stop entering the next glacial state?
>>
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About climate change: If the local climate can differ from global average temperature, does a global warming necessarily stop entering the next glacial state?
>>
can someone tell me where Im going wrong with this?

Q: classify (Z12 X Z4)/<(3,2)> according to the Fundamental Theorem of Finite
Abelian Groups

A:

<(3,2)> = {(0,0),(3,2),(6,0),(9,2)} = H, so ( Z12 X Z4)/<(3,2)> has order 12

(1,0) + H has order 6, so ( Z12 X Z4)/<(3,2)> is isomorphic to Z2 X Z6

but by FTFAG isnt it supposed to be isomorphic to something of prime power, not 6???
>>
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Does anyone here have link to Kunze's LA book which have Table of Content? I swear every single one I downloaded is just a shitty scan of the book.
>>13268958
>>13269083
You have to make your own thread for that anon, we only have mathfags, csfags, and physicists with the occacional biochem/medfags here.
>>
>>13266106
God i wish, the nu-right must die
also to /lgbt/ jannies: be faster
>>
>>13268870
use as many ghost cells as you need (that's usually stencil width/2), fill them by extrapolation of actual data according to your boundary conditions
>>
If a manifold M of dimension m has an atlas with only 1 chart does that mean M is diffeomorphic with R^m?
>>
>>13269158
Just take M = R^m - a point to see why this isn't true
>>
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I noticed when I do nofap I cum a lot more. Which naturally got me thinking does nofap increases the chances of multiple offspring from same pregnancy? If so by how much?
>>
>>13269204
Thanks, but I managed to find a better example.
>>
Let's say I have a function that shows the rate of water coming into a pool. If I want to know how much water is in the pool after 2 hours I would need to integrate, then insert 2 into the integrated function and I would get the answer.

What I don't understand is, why can't I just use a specific integral from 0 to 2 immediately? That gives a different, wrong answer. I don't really understand or see what the difference is.
>>
>>13269531
You need to add initial volume of the pool to the definite integral I think
>>
>>13269531
Integrating from 0 to 2 ignores the initial value (volume) assuming there is one to begin with
>>
>>13268271
I'll do it. Let me know payment and the subject, and when you need it done.
>>
>>13269549
>>13269553
Right, this makes sense. But then what I said before that is not true as well, right?
Inserting 2 into F(x) alone does not give the correct answer, it has to be F(2) - F(0)? They differ only in the beginning value, with the former being slightly bigger than the latter. But I have a hard time picturing what the exact differences are again, isn't it the same area?
>>
>>13269373
What is a better example?
>>
>>13269531
When you integrate from 0 to 2, the resulting function is V(2) - V(0), not just V(2).
>>
>>13269308
stop watching hentai
>>
>>13269556
F(2)-F(0) is the difference in volume between the initial moment and 2 hours later
F(2) is the total volume after 2 hours
>>
>>13269578
Thank you, now I get it.
>>
>>13269115
Anyone? I might buy/print the book myself if the ebooks are shit.
>>
If two observers A, B and C are accelerating in the same direction, but with different accelerations, are B and C going to observe the same fictitious force acting on A?
>>
>>13269671
Depends if you are talking about Newton or SR/GR. If Newton then the answer is yes otherwise no.
>>
>>13269671
three* obviously
>>13269682
If A has mass m and acceleration a_relB and a_relC according to B and C respectively, then isn't the fictitious force going to be either m(a_relB) or m(a_relC) in the opposite direction of movement, which differs in the Newtonian sense if a_relB and a_relC are nonequal?
>>
>>13269713
F=ma is not true in GR
>>
>>13269115
Thanks anon!
>>13269321
>>
I do not understand Diagonalization Argument / Proof of Cantor's Theorem. Any good links dumbing it down for a 99 IQ midwit
>>
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So are things in brackets matrixes? How are you supposed to figure out what to do with them? "OZ[1,Q+1]" came up in a paper I'm reading and I'm so lost.

t. dropout
>>
>>13269578
> F(2) is the total volume after 2 hours
F(2) is indeterminate because F includes an unknown constant of integration. You either need a reference point <t0,F(t0)> so that you can solve for the constant of integration, or you're limited to calculating differences F(t1)-F(t0) where the constant of integration will cancel.
>>
What's the lab technology behind DNA evaluation?
1) How is DNA (any kind) isolated from a sample?
2) How do they coordinate DNA? This shit is tangled as fuck, how do they know where they are on a chromosome?
3) How do they efficiently determine sequences on DNA?
When a test only costs a hundred bucks it can't be that time consuming.
>>
>>13269816
it's not even true in Newtonian mechanics unless a constant mass is assumed.
>>
>>13260699
Not an actual meme, why are people trying to get other people to eat bugs? I don't understand how eating bugs helps the enviornment.
>>
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Are these all equivalent? If not why not? Assuming the two areas with the negative sign before the integral are negative.
>>
Every time I try to start learning math I get unreasonably upset that it isn't statically typed. Writing the theorems down in Agda / Coq is about 100x easier to understand for me than in the fucking random ass notation of random ass .pdf.
>>
>>13270024
more nutritious value per ressource, at least that's what they claim.
>>
>>13270025
no, A, B abide a triangle inequality. A is equal to or greater than B. Which can be proven easily but is also immediately obvious when you think about it graphically. C clearly depends on the sign of the function in the specific region.
>>
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>>13270086
It's for this graph (the middle area being colored was for another exercise, ignore it).
I'm pretty sure C works but I don't really understand the difference between A and B.
>>
>>13270132
because b has the absolute value outside the integral
so -1 to 0 and 1 to 2 end up subtracting 0 to 1 thus the integral is smaller than A and C
>>
>>13270236
So for -1 to 0 and 0 to 1 the B one would give out negative areas, am I getting that right? What do the absolute value lines do then, nothing?
>>
>>13270247
1 to 2* I mean
>>
>>13270247
yes
it just takes the overpowering negative after the integral to be positive
>>
Good optimization mathematics textbooks? I already know the techniques and I want to get deeper into the math/intuition to better grok the material.
>>
>>13266984
>online
>masters
the only thing it's good for is pissing your money away. especially in a field like nuclear engineering, unfortunately.
>>
>>13270132
look at the integral of sin(x)dx over one period which is obviously 0. The absolute of sin(x) flips the negative part into the positive, so the integral of abs(sin(x)) over one period is 4.
>>
How do you prove the derivative of cos(x) is sin(x) without using the Taylor series?
>>
How do people sit on the floor in your country? Indian style? Indian style with one leg upwards? On their knees like nips? Ass and both feet on the floor, knees upwards?
>>
>>13269119
>God i wish, the nu-right must die
>also to /lgbt/ jannies: be faster
>>
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my physics fren told me energy isn't always conserved, can you guys give me examples of processes where total energy isn't conserved?
>>
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How does saturated steam produce hueg amount of work as it passes through a turbine? I understand the energy comes from phase change, but I don't understand why condensation would somehow make the turbine rotate harder.
>>
>>13260699
Had a terrible grade in an exam that is actually really easy, bottom of class. Know I could do better but no clue how, already study a lot and understand about 90% of the material.
Profs usually tell me I go too broad and don't pay enough attention to detail, how do I get better at that?
>>
ML question

If validation accuracy of my classifier starts oscillating around the same value for a few epochs, does it mean there's not point in training any further, or not necessarily and something can magically change later on?
>>
>>13270402
> How do you prove the derivative of cos(x) is sin(x)
It isn't; it's -sin(x).

> without using the Taylor series?
Well, using the Taylor series would be circular reasoning, given that you need to be able to repeatedly differentiate a function to find its Taylor coefficients.

Essentially, you start with the angle-sum identity:

cos(x+δx) = cos(x)cos(δx)-sin(x)sin(δx)
=> cos(x+δx)-cos(x) = cos(x)(cos(δx)-1)-sin(x)sin(δx)
=> (cos(x+δx)-cos(x))/δx = (cos(x)(cos(δx)-1)-sin(x)sin(δx))/δx
As δx->0, cos(δx)->1
=> cos(δx)-1 -> 0
=> (cos(x)(cos(δx)-1)-sin(x)sin(δx))/δx -> -sin(x)sin(δx)/δx
Also, as δx->0, sin(δx)->δx
=> -sin(x)sin(δx)/δx -> -sin(x)δx/δx = -sin(x)

This is a bit hand-wavy; it relies upon sin(δx)~=δx for small δx and (cos(δx)-1)/δx tends to 0 (i.e. the numerator approaches 0 "faster" than the denominator approaches 0).

For a rigorous proof, you'd need to use an epsilon-delta proof of the limit, which means being able to provide bounds on the difference between (cos(x)(cos(δx)-1)-sin(x)sin(δx)) and sin(x)δx.
>>
>>13270402
We start with a unit speed parametrization of the unit circle given by [math]\gamma (t)[/math], starting at [math](1, 0)[/math] and going counter-clockwise. We use it to define [math]\gamma (t) = (\cos (t), \sin (t) )[/math] (that is, we define sine and cosine with gamma.)
We then have [math]\| \gamma (t) \| = 1[/math]. Hence [math]0 = \dfrac{d}{dt} \| \gamma (t) \|^2 = 2 \langle \gamma (t), \dot{\gamma}(t) \rangle[/math].
Since [math]\langle \gamma (t), \dot{\gamma}(t) \rangle = 0[/math], we know that [math]\dot{\gamma}(t) = \lambda (- \sin (t), \cos (t))[/math]. The unit speed assumption nets us [math]\lambda = \pm 1[/math]. You then finish off with some sign analysis.

Does this work? No, because we assumed differentiability in the proof. See >>13270932 for what the real solution looks like.
>>
>>13270405
We don't sit on the floor.
>>
Is power engineering a meme as an undergraduate?
>>
How do I calculate this limit? I've tried, but I keep getting the wrong result. I haven't had any calculus in two semesters, I'm rusty.
>>
>>13271305
What result are you getting? Hospital's rule should work here
>>
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>>13271313
That's what I tried, still got something wrong along the way.
>>
>>13260699
what are the dangers of smoking out of aluminum foil
supposedly the oxide layer doesn't burn off and there's no ink so i'm wondering what the real dangers are
>>
>>13270932
Am I retarded or wouldn't it be much simpler to just prove the derivative of sin(x) first?

lim_h->0 (1/h)(sin(x+h) - sin(x))
= lim_h->0 (1/h)(sin(x)cos(h)+sin(h)cos(x) - sin(x))
= lim_h->0 (1/h)(sin(x)(cos(h) - 1) + sin(h)cos(x)) = cos(x)

Then use the fact that cos(x) = sin(pi/2 - x), differentiate sin(pi/2 - x) with respect to pi/2 - x which yields cos(pi/2 - x) = sin(x) and multiply by the derivative of pi/2 - x which is -1
>>
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>>13263328
You want any help anon? Have you covered the isomorphism theorems yet?
>>
>>13271748
He's already left. See >>13264378
>>
>>13260699
Guys please help me with this proof.
Proof that any even square number is a multiple of 4.


I looked online and all they did was proved that any even number squared is a multiple of 4, which is different.

I know it is easy, but I am retarded.
>>
>>13271857
It's the same thing. Square numbers are numbers that can be expressed as the square of an integer.
>>
>>13271873
>>13271873
I guess I have trouble seeing the formal proof.

Given integers N, X, and Y, where N = 2X, and N = Y*Y, proof that N mod(4) = 0.
>>
>>13271857
(2n)^2=4n^2
(2n+1)^2 = 4n^2+4n+1

The square of an even number is even, the square of an odd number is odd. Consequently, if a perfect square is even, it's the square of an even number and (as you've already noticed) the square of an even number must be a multiple of 4.

IOW, any square is either a) a multiple of 4 or b) odd.

Also: as can be seen from the above, any square must be congruent to either 0 or 1 modulo 4. So it can't be congruent to 2, i.e. it can't be a multiple of 2 without also being a multiple of 4.
>>
>>13271936
Thanks!
>>
What's a good book to learn AS level mathematics?
>>
>>13271339
Looks fine to me. Why do you think you got something wrong?
>>
I have two sets [math]I[/math] and [math]B[/math]. Each element from [math]I[/math] can be given to a subset from B. How would I find the smallest subset [math]A \subseteq I[/math] so that every member of B gets at least 2 with a Branch-and-Bound approach?
Is there any known algorithm out there which is used for such cases? I cannot think of where to start here
>>
Is anyone familiar with the ti nspire cx ii-t calculator?

I want to calculate the interval where a graph is 15, but it only gives me the start of the interval, not the end. On the graph I can clearly see it hitting that value twice however. I do
nSolve(f(x)=15,x)
Anyone an idea?
>>
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Does anyone understand why is the range of values [-sqrt(y),sqrt(y)] and [-1,sqrt(y)] used for the two Ay cases respectively? Thanks
>>
>>13266780
How to get back
>>
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please just explain to me how the fuck is the matrix that way when projecting xyz to uv screen why what the fucking fuck
>>
>>13272905
It is a particular perspective projection / transformation but unfortunately the answer isn't neither simple or short. So unless you accept "that's just how combining multiple rotation matrices be bro" and it's just the convention to use a left-handed coordination system then you need to read

general form of the transform - https://en.wikipedia.org/wiki/3D_projection#Perspective_projection

the uv specific transform - https://www.programmersought.com/article/76735494361/
>>
If A(x) is a 2 x 2 matrix, what the hell is this supposed to mean?
>>
>>13272541
Can you ask the question again, but in english this time?
What the fuck do you mean "can be given"?
>>
>>13273239
[math]A(0)[/math] is a two by two matrix. Hence, matrix multiplication.
>>
>>13273239
Its just standard matrix multiplication. So A(0) is some matrix such that

[math]
A(0) =
\begin{pmatrix}
a_{11} & a_{12} \\
a_{21} & a_{22}
\end{pmatrix}
[/math]
where in general each component [math]a_{ij}=a_{ij}(x)[/math].

So that equation is the same as writing the two equations

[math]
\begin{align*}
a_{11}(0)\ p + a_{12}(0)\ q &= 6 \\
a_{21}(0)\ p + a_{22}(0)\ q &= 6 \\
\end{align*}
[/math]
>>
Hey, just cramming some math rn and I have a few quick questions to make sure I have the right idea about some stuff. If someone could just say yes or no that would be killer.
1) The fundamental theorem of line integrals works because the fact that field $f$ is conservative means that the vertical change sort of cancels out , and the fact that $r’(t)$ is a vector means that any time a path diverges from the straightest path between points a and b, it must go back in the opposite direction, thus cancelling out the change
2) A scalar line integral can be thought of as the area under some function integrated along some arbitrary path in the domain of that function, a vector line integral is more like a vector sum with each vector adjusted to get its component which lies on the path C at a given point.
3)a flux integral just sort of describes the total speed at which some vector field $f$ is moving at perpendicular to some surface $s$
4)this might be a very stupid question, but it seems as though most of the theorems in vector calculus are predicated on any vector field in the equation being sufficiently smooth. Please correct me if I’m wrong on that, but it seems like it must be a necessary piece to things like the divergence theorem functioning
5) Stokes theorem. I’m embarrassed to say I’m having a lot of trouble seeing how it works, but my assumption is that it kind of functions similarly to the divergence theorem because the fact that it must be smooth means a lot of different axes of flux end up cancelling out and the end result is that the total remaining flux is equivalent to the path along the curve encompassing the surface.
Apologies if these are stupid questions, I only started vector/multivariable calculus yesterday and I’m trying to finish learning it by tonight.
Thanks!
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>>13273394
Btw for question 3 I meant to include the analogy of like a metal gate in a river. The water doesn’t necessarily move that metal gate (in the ideal setting) but the water flowing through the net has some total speed. Sort of like the surface isn’t really a surface and more like an invisible surface which exists (at least within this single calculation) to describe exclusively fluid flow.
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>>13273394
Those should be alright
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>>13272882
does this help? https://www.desmos.com/calculator/vhwcsqyrsy
you can move the slider in the top left
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>>13273535
Thanks man!
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can any mathfags explain why is it so hard to prove fermat's last theorem? isnt this basically just a generalized pythagoras formula?
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Please can somebody tell me if destructive interference genuinely means the actual resulting sound wave is a quieter one due to physics, or if it's some kind of trick?
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>>13273947
Well that's why it became so famous. Incredibly simple to state that even non math-fags could understand the question but every method people tried for 300 years failed.
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>>13273964
Sound waves occupy 3D space. You'd need to position yourself correctly relative to the sources if you want them to destructively interfere.
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>>13274017
So it actually is real then? Active noise cancellation means my ears receive a quieter sound or no sound at all, because the combination of opposite loud sounds is turned into no sound?

Or are both sound waves still hitting my ear drums.
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>>13274017
>>13274029
So sound is just vibrations of air. When two "opposite" sounds interact, instead of making those atoms vibrate more it makes them not interact at all. Yes it works, you could vibrate a piece of steel on one end and then vibrate it with the opposite soundwave on the other end, the result would be a completely still piece of steel.
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>>13270375
k
I want a PhD and a real job. Part timing seems like the way to do that
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>>13274029
Yes its due to physics, waves that are 180 degrees out of phase with each other cancel out. In a sense yes its both sound waves hitting your ear. But really the way to think about it is that your ears functionally only record a single waveform. That waveform is the result of all vibrations in the air combined together. So what really happens is that the phase canceled waves just neutralize and don't get added in to the final waveform that actually hits your ears. Its not like sound is a bunch of different waveforms all at once, rather they are all condensed into a single waveform.
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>>13274125
So the eardrum is vibrating less or differently because it the additional waveforms hitting it? So could this cause hearing damage since it's actually more waves hitting the eardrum.
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>>13274134
shitty bait but just in case you're actually a 5 year old...

How many different sources of waveforms don't matter, just the total combined amplitude; How loud a sound will be is independent of the number of sound sources.
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>>13274141
I don't get how it's shitty bait, sorry for not understanding. Read the title of the thread.
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How to differentiate floor/ceil functions?
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>>13274157
can't
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>>13270458
there are two answers to this question depending on your level of understanding.
in classical mechanics, energy IS always conserved. however, sometimes the energy changes form. for example, you can't use conservation of energy principles when solving problems including friction, because the frictional force dissipates some of the energy into heat. if you were to add the heat energy into the equation, you would find that total energy is conserved, just not motional energy on its own.

in quantum mechanics, there is something called the "energy-time uncertainty relation," which is like the heisenberg uncertainty principle but for the variables energy and time. so, for processes that happen extremely quickly (e.g. interactions between subatomic particles) there are steps of these processes that happen in such a short amount of time that there is a large uncertainty in the energy of these steps relative to the total energy of the system. so things that would be forbidden by energy conservation (exchange of a massive boson that has a larger mass than the energy of the collision, for example) are allowed as your energy uncertainty encompasses a range of possible energies greater than what you started with.
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>>13273964
its no trick, waves do really cancel each other out resulting in silence (if done perfectly). I believe noise-cancelling headphones use this method to.. cancel noise around you.
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>>13274157
Alternatively, impulse train
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How do I learn faster with textbooks? Sometimes I feel I wasted too much time working on easy obvious problems of the book.
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>>13274157
Dirac comb

Formally, floor/ceil aren't differentiable as the limit (of (f(x+δx)-f(x))/δx) from above and limit from below differ. One is zero, the other is infinity.
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Is there a word for when someone is being pedantic, but they're not being pedantic enough, so they're basically just incorrect?
Like the Remark in https://en.wikipedia.org/wiki/Dirac_comb#Fourier_series
, to quote:
>Remark: Most rigorously, Riemann or Lebesgue integration over any products including a Dirac delta function yields zero.
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>>13274305
idk mistaken?

can you give some more examples? maybe even a hypothetical?
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>>13274328
>can you give some more examples?
Like if someone criticizes an engineering or physics proof because it disregards one possible situation when this situation is discarded because it's physically irrelevant.
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why do crops need to get their nitrogen from fertilizers? can't they just bind free nitrogen in the air?
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>>13274790
1. N2 gas is not directly usable in the plant energy cycle because:
2. breaking N2 gas is energy inefficient without specific enzymes
3. these enzymes don't work well in the presence of oxygen, so plants never evolved to use them themselves as bacteria in the oxygen-poor soil ended up doing most of the work
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>>13274854
>>13274790
I forgot the important point, plants need ammonia NH3 which they can use and is not found in the air.
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>>13274239
The more time you spend on a problem (i.e. actually thinking about it, not just procrastinating), the more you are learning.
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Can some one please help me understand the relationship between upper triangular matrix and eigenvalues. For example
of the matrix

2 1 2
0 2 -1
0 1 0

I think the eigenvalues are -1,1,2 because when row reduced you get

2 1 2
0 2 -1
0 1 0
- >

2 1 2
0 1 0
0 0 -1


You get an upper triangle diagonal matrix so the eiganvalues must be the numbers on the diagonal.
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Is there a CAS/symbolic math program that /sci/ recognizes as generally superior to others? Should I just get WA pro?
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>>13273283
Sorry for the bad wording.
Meant something like the set [math]I[/math] being fruits, and the set [math]B[/math] being people (who like certain fruits). How would I go about the minimal set of fruits so that each person gets at least 2 they like? I don't see any way to properly Branch, nor Bound
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>>13274971
mathematica if you have a free uni license (or manage to "find" a free version)
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Is higher level math as hard as it looks or it just a matter of knowing the different symbols and concepts. Do you have to be high iq
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>>13274978
Ah, I see.
Maybe you need to run through I, opening up a new branch at every choice of "removing this element or not"?
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>>13274998
But that would be the same as brute forcing it, no?
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>>13275005
Quoting wikipedia,
>A branch-and-bound algorithm consists of a systematic enumeration of candidate solutions by means of state space search: the set of candidate solutions is thought of as forming a rooted tree with the full set at the root.
In other words, branch and bound is pretty much methodical brute-forcing.
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>>13275015
Ah yes, but brute-forcing isn't the same as Branch & Bound though
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>>13275049
Yes, and >>13274998 isn't quite brute-forcing either.

You could also, alternatively, order the B's from smallest to largest and then branch and bound by each choice of addition.
Clearly not equivalent to brute-forcing either, as you can tell if one of the elements of B only has two elements.
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any mechanical engineers? how exactly do i take the angular impulse of pic related about the point B? I looked up the answer and they had that the moment of inertia about b was the the moment of inertia of the center of gravity MINUS the mass times the distance to the pivot point squared. why is it minus?
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>>13275056
Is it because the velocity is downward and then the velocity is upwards after it strikes point B?
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>>13274328
I've just come across another example on /a/.
See https://en.wikipedia.org/wiki/Mass_in_special_relativity#Relativistic_mass
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if pic related is true, how come it wouldn't also apply to males?
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>>13275203
Oh, but it does... There's a story of this young Roman that was the popular cumdump of the entire army, and when he grew up, he became a legendary mr. steal-yo-girl stud.
Anecdotal, but interesting if true.
Perhaps this is why the elites put the ban on homosex, they don't want any more ubermenshes being created to threaten their power. We know it's what they all do behind closest doors, among other activities.
>LOL most fags of today are söy as fuck
That's why there's such an effort to modify and corrupt our genetics through various means, especially the male traits.
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>>13275270
so then every straight male accrues secondary contamination from every woman he has sex with, and tertiary contamination from every man that woman had sex with, and...
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>>13275291
It's well known that testosterone drops the more a man has sex or masturbates. In terms of becoming contaminated by fucking roasties, that's trickier...
If she was selective to high quality genes, it wouldn't necessarily be a bad thing.
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>>13275270
this reminds me of how in Rome, the most emasculating sexual act a man could perform was cunnilingus. like it was more manly to take it up the ass than to eat a woman out. perhaps the ancients knew something that we're slowly re-deriving.
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>>13274948
For a triangular matrix (upper or lower), the entries on the diagonal are the eigenvalues. More generally, for a triangular matrix the determinant is the product of the diagonal entries. So the characteristic polynomial of A = |A-λI| is the product (a_1,1-λ)(a_2,2-λ)...(a_n,n-λ) and its roots are the diagonal entries.

That says nothing about the eigenvalues of some matrix which can be row-reduced to a triangular matrix, as row-reduction changes the eigenvalues. Any given matrix can be reduced to infinitely many different upper-triangular matrices (all of which are equivalent up to a scale factor applied to each row), and each different upper-triangular matrix will have different eigenvalues.
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>>13275118
id call that person ignorant and pompous
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>>13275319
>It's well known that testosterone drops the more a man has sex or masturbates.
Source?
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>>13275319
> It's well known that testosterone drops the more a man has sex or masturbates
Completely not true.
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>>13270025
Only A and C compute the same thing.

To understand, note that integration is a summation (read the definition of the Riemannian sum), so it all breaks down to the fact that |a + b| != |a| + |b|
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What are standard practice tests for polymer biodegradability? Anyone got some papers/books for biodegradability 101?
>>
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Is it worth going for an regular engineering degree? Should go for a specialization like we or me?

I had trouble understanding physics even though I ended up with an A.



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