/sqt/ /qtddtot/ - stupid questions thread

[Anonymous No.12796332]

Previous thread: >>12777391

>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?
>>/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/
>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/JY6NNeL
https://imgur.com/a/0qDEgYt
>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
>If you use j for the complex unit, put a ¿ somewhere in your post or use emoticons I will automatically ignore your question. I don't actually know about everyone else, but you shouldn't assume they're too far off about whatever random things they dislike

[Anonymous No.12796371]

Why is j squared negative one

[Anonymous No.12796401]

What does "S = k. log W" mean?

[Anonymous No.12796403]

>>12796305
> What does the '\' mean? It erases the semicolon?
It causes the semicolon to be interpreted literally rather than being interpreted by the shell (the semicolon is used to separate commands). Enclosing the semicolon within quotes (single or double) would also work, but for single characters using a backslash is less typing.

Without any quoting or escaping,
sort -t; -k3 ...
would cause the shell to interpret that as 2 separate commands, and it will complain that there isn't a program named "-k3".

[Anonymous No.12796406]

>>12796223
>>12796223
> How do you know it's not a rectangle or a rhombus?
If you're asking whether the quadrilateral can arise from a combination of rotation, translation, uniform scale, and perspective projection (no non-uniform scale or skew), once you've computed the 3x3 matrix, you need to determine whether it can be expressed as
[eqn]
\begin{pmatrix}s x_x & s x_y & s x_w \\ s y_x & s y_y & s y_w \\ z_x & z_y & z_w\end{pmatrix}
[/eqn]
where the vectors
[eqn]
\begin{pmatrix}x_x \\ y_x \\ z_x\end{pmatrix}, \begin{pmatrix}x_y \\ y_y \\ z_y\end{pmatrix}
[/eqn]
have unit length and are orthogonal. So find a value of s which satisfies one of the constraints and check that the other two hold. E.g. for the orthogonality constraint, you get s=sqrt(-(c21.c22+c11.c12)/(c31.c32)). Substitute that into (c11/s)^2+(c21/s)^2+c31^2=1 and (c12/s)^2+(c22/s)^2+c32^2=1.

[Anonymous No.12796413]

>>12796332

Say if brain computer interfaces become commonplace and they can be used to regulate brain chemicals,
what would a naked intelligence look like in groups of humans, if their emotions weren't easily influenced?

[Anonymous No.12796567]

why jet fighter pilots experience high g forces when they are not always accelerating?

[Anonymous No.12796572]

>>12796401
W is something like the possible states your system can be in.
Because that's usually a fuckhuge number you take the log of it, multiply it by a constant and call it entropy

[Anonymous No.12796578]

>>12796332
Do programming socks actually work?

[Anonymous No.12797009]

>>12796332
So a external magnetic field induces a ring current in a ring superconductor and since the resistance in a super conductor is negligible the current would never dissipate.
Is it therefore possible to capture an external magnetic field and convert/make us of said field without any loss? Is this used for energy storage?

[Anonymous No.12797029]

>>12796578
41% of the time

[Anonymous No.12797067]

Linux Question

I'm trying to get all Monday the 1st of any year and can't use awk.
Ñ
I tried cal -y | grep 'Mo 1" , no luck what else can I try my brain is fried already

[Anonymous No.12797092]

>>12797067
Do you have to use "cal"? Otherwise, I'd use "date" in a loop, e.g.
for month in 01 02 03 04 05 06 07 08 09 10 11 12 ; do date -d "2021-$month-01" ; done | grep '^Mon'
Use -I to change the output format.

[Anonymous No.12797128]

>>12797092
I can use that one two, I cant seem to make t work, any how I need to do that then print the number of time it happens, I think piping it with uniq -c could work right? Or grep -c

[Anonymous No.12797148]

Is 2e^2x and 2xe^x^2 identical? If I derivate as usual I get the former result but the latter is what the answer is marked as. I assume they're identical but I can't tell where that x outside of the exponent came from.

[Anonymous No.12797158]

>>12797148
No

[Anonymous No.12797162]

>>12797158
f(x) being (e^x)^2, forgot to mention. Wolframalpha seems to agree with my result, so unless the answer sheet is wrong they have to be identical?

[Anonymous No.12797166]

>>12796332
QM fags: is there a way to succinctly explain wave function interference? I understand the surrounding concepts, but I'm struggling to grasp exactly how it occurs. Fundamentally the wave function has no... physicality. In what way does it truly "interfere" if it's unreal to begin with?

[Anonymous No.12797171]

>>12797166
re: My instinct is this is just another mathematical quirk glossed over with language that implies physical action

[Anonymous No.12797176]

>>12797162
In that case then yeah you're right, the latter is the derivative of [math]e^x^2[/math] which is not the same thing.

[Anonymous No.12797184]

>>12797162
You're doing something wrong. The derivative of (e^x)^2 using the chain rule should not give you an x out front. It would if it was the derivative of e^(x^2), but that's different.

[Anonymous No.12797214]

>>12797166
>Fundamentally the wave function has no... physicality.
Neither has energy.
That's a stupid thing to object to.

[Anonymous No.12797245]

>>12796578
I will literally hit on you if you wear them, but,
>>/g/

[Anonymous No.12797250]

Linux

Ok why can I get the number of Friday 13 but when I change the settings to see the number of Monday 1st in a year, it doesn't work.

ncal 2021 | grep 'Fr' | grep -o 13 | WC -l

[Anonymous No.12797265]

>>12797250
Works for me, with lower case wc

[Anonymous No.12797267]

>>12797265
ncal 2021 | grep 'Mo' | grep -o 1| wc -l

So it gave you 2? That's the right answer, I'm getting 21

[Anonymous No.12797272]

>>12797267
>ncal 2021 | grep 'Mo' | grep -o 1| wc -l
ncal 2021 | grep 'Mo' | grep 1
Try this and you'll see your error

[Anonymous No.12797276]

>>12797250
You a first-year student or something?

[Anonymous No.12797282]

Why doesn't anyone talk about nuclear fusion anymore?

[Anonymous No.12797283]

>>12796332
Does ANYBODY in molecular biology use LaTeX? I remember being told on 4chan so many times that all scientists typeset manuscripts in LaTeX but here I am but every professor and post doc researcher I know without exception uses Word.

[Anonymous No.12797303]

>>12797272
I meant 1947 should give me 2 but it gives me 21.
I can't see the error nigga, help a brother.

>>12797276
Yes. Never done cs before and my professor has given us difficult commands to use that we haven't used before mixed with their options.

[Anonymous No.12797316]

>>12797303
Not sure if you know this but there is a thread on /g/ dedicated to Linux by the name of '/fglt/ - Friendly GNU/Linux Thread', you'd likely find more variety of answers there since I don't imagine many people here have experience with Linux.
I'm not saying that you shouldn't ask here, don't get me wrong, but you'd have a bigger pool of experienced people to ask. /g/ also has their own /sqt/ equivalent. Good luck anon

[Anonymous No.12797330]

>>12797303
You output every 1 in your dates. 1, 11, 21, etc
ncal 2021 | grep 'Mo' | grep -o " 1 "| wc -l
should work

[Anonymous No.12797333]

sqrt(e^x) = e^x/2 = e^x1/2 is all the same, correct?

Is this derivative right or did I mess up somewhere? x/2*e^x/2-1 ?
I want to get to e^x/2sqrt(e^x) but am not sure how with my answer there, so it's probably wrong somewhere.

[Anonymous No.12797340]

>>12797316
>>12797330
Really appreciate it guys. I'll take a look there.
Yes, it worked.

I can't seem to make sense of the " 1 ". My professor didn't explain shit and told us straight we'd have to work with things she didn't show us.

[Anonymous No.12797348]

>>12797340
A "1" is in "1","14","14532"
A " 1 " isn't because of the whitespace

>>12797333
>e^x1/2
Do you mean e^(x^(1/2))?
If so, no

[Anonymous No.12797349]

>>12797333
Apply the chain rule. The derivative of [math] \sqrt{f(x)} [/math] is [eqn] \frac{f'(x)}{2\sqrt{f(x)}} [/eqn]

[Anonymous No.12797352]

>>12797340
>I'll take a look there.
Give it a try, my issue with programming is that there are 50 ways of doing the same thing, maybe that isn't the case with Linux, I have no idea, but the more answers you can get, the more diverse your applications can be. The only reason why I suggested you them was that they actually looked friendly so try your luck.
>My professor didn't explain shit and told us straight we'd have to work with things she didn't show us.
Absolute state of educayshun

[Anonymous No.12797358]

Did everyone leave?
sqt doesn't feel like how it used to be.

[Anonymous No.12797361]

>>12797358
Its Saturday morning dumbass.

[Anonymous No.12797363]

>>12797358
Maybe people got smarter

[Anonymous No.12797365]

>>12797361
You're right.
>>12797363
Guess I'm still dumb

[Anonymous No.12797372]

>>12797352
And she isn't allowing us to use awk or sed which seem to be relevant.

This shit is 15% of the final grade, and she has policies of only 1 extra day for late work. After that you get a 0.

[Anonymous No.12797403]

Question towards anybody that has studied physics or is currently studying physics.
What is your recommended ratio of hours studying to hours doing exercises ?

[Anonymous No.12797407]

I posted this on /scg/ but I wanted to ask here as well if that's okay. Reddit spacing so that it is easier to read, don't bully me.

>College offers a bunch of opportunities
>Limits them to ONLY underrepresented minorities in the STEM field like hispanics/blacks/native americans
Is there a way to actually get them without having to race change?

Is the standard procedure to getting research opportunities or internships in general, to build up a relationship with your professor until they go "You know anon, it's been a while since we started talking, I have an opportunity and I'm not sure if you're interested........"

It seems like that'll take a long time but at this point, I wouldn't even mind because I have some wonderful professors but it feels a bit disingenuous (or even a bit... messed up) to build a relationship with someone just because they're a door of opportunity or is that just how STEM works in general? I'm an EE major btw.

I know that if you genuinely want to learn from them and build up a relationship, then it would no longer be disingenuous, but I know that not every professor I come across would be as wonderful/cool as some of the ones that I'm taking currently which would make it far less interesting for me to want to go out of my way to learn more/go ahead.

[Anonymous No.12797421]

>>12797283
>all scientists typeset manuscripts in LaTeX but here I am but every professor and post doc researcher I know without exception uses Word
Anon.. I..

[Anonymous No.12797423]

>>12797403
>What is your recommended ratio of hours studying to hours doing exercises ?
I've been only doing/copying homework and learning ~1 week before a hard test and 3 days before an easy one.
I took me nearly double the usual time to get my master's.
Many of the shut up and calculate tests really fucked me because I simply was too slow.
On the other hand I'm living the neet lifestyle without being a neet, which is nice

[Anonymous No.12797427]

>>12797407
If you're White or Asian your only bet to succeed is to build relationships because everything will be stacked against you

[Anonymous No.12797458]

>>12797407
The professor doesn't have to be the one to bring it up. If they're doing something that you're interested in, just ask them to talk about that - they'll usually say yes, professor like talking about their work. e.g.

"Hi Professor-sensei,

Hello, I am Anon-kun, a [cohort] EE major. You might remember me from [class]. I remember towards the end of the class, you mentioned how [technique] applies to [problem]. I thought that this sounded fascinating, and after looking at some of your publications in [topic], I've become really interested in [work].

Is there a time in the next couple of weeks we could meet to talk about your research?

All the best,
Anon-kun"

Meet with the Prof, talk about their work for however long, and then towards the end ask if there are any projects they're working on in that topic that you could help with. That's how I got involved in research anyway.
>t. half white half asian heterosexual male

[Anonymous No.12797479]

>>12797458
>Is there a time in the next couple of weeks we could meet to talk about your research?
You think profs have time for that?
They have to deal with bureaucracy, office politics and their classes. Sometimes you only get to their secretary

[Anonymous No.12797510]

>>12797479
Worked for me. I got a 2/3 success rate, while the 1 who couldn't make it work was about to go on maternity leave and said to email her next quarter if I still had time. Though my school isn't that big so the profs probably have more time for undergrads in general.

Plus, talking about their work to a captive interested audience is the fun part for the professors. They wouldn't have become professors, a terribly stressful job, if they don't find their research interesting, and don't like talking about things they find interesting. Excluding tenured grumpy old farts, of course.

[Anonymous No.12797529]

>>12797427
>to build relationships because everything will be stacked against you
I just have to come to terms with it at this point. A good black friend of mine got an internship at a dream company as well as a research position through one of those minority societies/offers, while I'm genuinely happy for him, a small part of me feels jealous. Thank you anon. Just need to try harder!
>>12797458
>If they're doing something that you're interested in
Is there a way I can find out what they're doing without having to ask them directly? You mentioned publications, so I'm thinking I might need to google their name on google or something but no website name directly comes to mind on where to find them. IEEE, I guess? But if they published it, they're probably done... Maybe I just have to actually email them or ask them to talk more about it like you mentioned.
Apparently, they're doing hydrogel reaction research but I have no idea how that relates to engineering (though this is probably where I can do some additional research and learn more!)
Thank you and I hope you got your dakimura senpai, unless I'm remembering you for someone else.

[Anonymous No.12797563]

>>12797529
Sometimes your university will have an online resource for finding professors by research topic, and you can find publications there too. Otherwise, you can look up them up through IEEE or google scholar. As long as the paper is fairly recent, your prof is probably still working on further problems in the same topic, or using the same methods / approaches from that topic in another field, so don't worry about your prof "being done" - research is never really done, after all!

And yes kouhai, that's me. I've contacted the right people and the dakimura is currently in the works.

[Anonymous No.12797626]

Is it possible to convert heat in the vacuum into some for of energy (kinetic, electric, light) to deal with cooling?

[Anonymous No.12797683]

>>12797283
>Does ANYBODY in molecular biology use LaTeX?
Probably.
Like, Word is comfy, but if you have a [math]\text{preferred text editor}[/math] then you'll inevitably prefer Latex or Markdown or whatever the fuck people use these days over Word.
And there's probably at least one person in molecular biology who has a [math]\text{preferred text editor.}[/math]

But someone was lying boldly to you if they told you people outside of maths and mathy stuff use Latex.
>>12797361
Saturday morning is optimal homework solving time.

[Anonymous No.12797699]

>>12796371
Its a definition to allow for complex numbers to be used.

[Anonymous No.12797700]

>>12797626
>heat in the vacuum
What heat?

[Anonymous No.12797705]

>>12796567
They can only experience g-forces under acceleration, but this acceleration does not only have to be linear. Curves induce a centripetal acceleration that would cause g-forces.

[Anonymous No.12797710]

Is there a website that allows me to crash waves into reflective barriers and see how they behave?

[Anonymous No.12797711]

>>12797700
Sunlight heat, internal heat from spaceship engine, whatever.

[Anonymous No.12797718]

>>12797711
No idea what you're asking
Probably not

[Anonymous No.12797722]

>>12797349
Hm I've been trying for a while but I can't figure it out. I'm getting to here:

= e^x/2 = e^1/2x
= 1/2 * e^1/2x

But I'm kinda confused how to continue this to get to e^x/2sqrt(e^x). Is there something I can look at with the exact example of sqrt(e^x)? I'm seeing similar things that I can figure out but not this exact case.

[Anonymous No.12797733]

>>12797722
>1/2 * e^1/2x
That's the answer though
f' = e^x
1/f = 1/sqrt(e^x) = e^(-x/2)
1/2 * f'/f = 1/2 * e^(x/2) = 1/2 * sqrt(e^x)

[Anonymous No.12797751]

>>12797722
Sorry anon, I didn't read your question carefully enough. Your expression is correct. Assuming I'm reading your notation correctly, the answer key has this as the answer: [eqn] \frac{e^x}{2 \sqrt{e^x}}. [/eqn] However, this can be simplified like so: [eqn] \frac{e^x}{2 \sqrt{e^x}} = \frac{e^x}{2 e^{\frac{1}{2}x}} = \frac{1}{2} e^{(x - \frac{1}{2}x)} = \frac{1}{2} e^{\frac{1}{2}x}. [/eqn]
Which is exactly your answer. Are the above manipulations clear?

[Anonymous No.12797754]

>>12797563
>Sometimes your university will have an online resource for finding professors by research topic
Good reminder! I think the best place would be to ask the librarians in my college, would have to find their zoom link / email now because of the rona.
>research is never really done, after all!
Heh, can't believe I forgot about this, it's so obvious afterall--maybe it's not as obvious since I forgot that research never really ends...
>dakimura is currently in the works.
It seems like you went above and beyond! Even comissioning a personal work it sounds... Hope it's a character you genuinely like and keep us updated! Don't go down the rabbit hole!

[Anonymous No.12797789]

>>12797733
Ok it being correct is a relief. But now I want to write it "nicely" with the root stuff as a single thing.
>>12797751
No need to apologize! I'm glad you're helping in the first place.
I'm not exactly sure what you're doing there. I'm starting at the last step and going left, but can't figure where that x in (x-1/2x) is coming from or why there's suddenly both a e^x at the top and bottom of the fraction afterwards.

[Anonymous No.12797798]

>>12797333
[math]\frac{d}{dx}e^{\frac{x}{2}}\underbrace{=}_{y=\frac{x}{2}}\frac{dy}{dx}\frac{d}{dy}e^y=\frac{1}{2}e^{\frac{x}{2}}[/math]

[Anonymous No.12797850]

>>12797789
>>12797789
Honestly, your answer is more concise and cleaner, which is why going from right to left has some funny looking steps out of nowhere (such as [math] e^{\frac{1}{2}x} = e^{x - \frac{1}{2}x} [/math]. I'll go through each manipulation from left to right, since it's a little easier to see the motivations that way.

We start with [eqn] \frac{e^x}{2 \sqrt{e^x}}. [/eqn] Recalling that the square root operation is equivalent to raising the input of the root to the 1/2 power, this simplifies to [eqn] \frac{e^x}{2 e^{\frac{1}{2}x}}. [/eqn] Then we recall the fact that [math] \frac{1}{a^b} = a^{-b} [/math] for arbitrary a and b, so the second expression becomes [eqn] \frac{e^x}{2 e^{\frac{1}{2}x}} = \frac{e^x}{1} \frac{1}{2 e^{\frac{1}{2}x}} = \frac{1}{2} \frac{e^x}{1} \frac{1}{e^{\frac{1}{2}x}} = \frac{1}{2}(e^x e^{\frac{-1}{2}x}). [/eqn] The last step just involves simplifying exponents that have the same base, so [eqn] \frac{1}{2}(e^x e^{\frac{-1}{2}x}) = \frac{1}{2}e^{x-\frac{1}{2} x} \frac{1}{2}e^{\frac{1}{2}x}. [/eqn]

Did that make sense?

[Anonymous No.12797854]

>>12797850
fuck missing an = sign in the last step, should be [eqn] \frac{1}{2}(e^x e^{\frac{-1}{2}x}) = \frac{1}{2}e^{x-\frac{1}{2} x} = \frac{1}{2}e^{\frac{1}{2}x}. [/eqn]

[Anonymous No.12797925]

>>12796332
I don't get it.

[Anonymous No.12797954]

>>12797754
>Hope it's a character you genuinely like and keep us updated!
Will do. It's going to be a long process since the art has to be made, a bit of back and forth for comments, then printed onto the case & shipped over to the states. I also wouldn't say I went above and beyond... [math] _{ {_\text{since my waifu is an OC}}} [/math]

[Anonymous No.12797979]

>>12797850
Being honest, no. I'm getting closer but parts aren't making click. This all seems very convoluted compared to what I did, as you pointed out, I don't know why it's the example answer. I think I'll put it to rest for now since I at least got the correct answer, even if not in the desired form. Gonna take a jog and try again with a fresh mind. Thank you for the explanations.

[Anonymous No.12798013]

>>12797283
look into mhchem

[Anonymous No.12798020]

>>12797626
you can transfer energy in vacuum through radiation

[Anonymous No.12798042]

>>12797925
I am illiterate. So I apologize.

These highlighted sets of S are the same set, and that's where the contradiction comes from?

I assumed they were different (since you'd get contradiction if they were the same and that'd be ridiculous who would do such a thing)

[Anonymous No.12798060]

Can someone confirm this:

There must be 181 latitude degrees on a sphere/earth as we have 90:0:-90

There must only be 360 longitude degrees on a sphere/earth because -180:0:180 but -180 and 180 are the same so it is actually -179:0:180

[Anonymous No.12798079]

Anybody got some tips on how to work your way through a math book?
I'm currently going through Abbott's "Understanding Analysis" (asked for help here a few times) and it went alright until the chapters on series, which kinda filtered me. Before that, I usually could do at least half the practice problems and generally had a somewhat correct intuition for the rest, but could barely get anything correct on the series exercises.
Currently, I put definitions/theorems/lemmata in Anki so I can memorise them and work through the proofs until I understand them. Anything else I can do to really get the material and be able to apply it better?

[Anonymous No.12798094]

>>12798079
What I typically do is return to the first chapter again and re-do all the problems from the beginning until I reach the point where I got stuck before.

Give your brain some time before returning to series again.

[Anonymous No.12798115]

>>12798094
i thought about doing that after i go through the whole book (maybe even more than once) to fill in the gaps, but maybe it makes more sense to take an incremental approach at this point already
thanks for the idea!

[Anonymous No.12798141]

bumping my question about molecular orbitals and how they "look" >>12791601

[Anonymous No.12798208]

>>12798060
> Can someone confirm this:
> There must be 181 latitude degrees on a sphere/earth as we have 90:0:-90
I can confirm that you're wrong. 90-(-90)=180. There are 181 distinct integer latitudes, but that's not the same thing. In the same vein, a 10-metre tape measure isn't 11 metres long because it starts at 0 and ends at 10.

> There must only be 360 longitude degrees on a sphere/earth because -180:0:180 but -180 and 180 are the same so it is actually -179:0:180
No, it's (-180,180] or [-180,180), i.e. a half-open interval. Either way, it spans 360 degrees. If it was -179..180, -179.5 wouldn't exist.

[Anonymous No.12798232]

>>12798208
Thank you mate
But if we assume that we only plot a point for every integer latitude / longitude combination, we can exclude longitude integer -180 since we are plotting points for longitude integer 180, right?

[Anonymous No.12798252]

>>12797954
>That super small font
Lil' shy aren't you senpai... You'll get used to it sooner or later! Especially when your parents see it, then you'll start to shed some of the embarrassment away until you're just you! Also having one of your OC made is quite literally above and beyond, especially if you're putting it on a daki, good job! I just hope that you don't buy onaholes anytime soon... I think that even if you don't turn out to like the daki in the end, you'll feel much better because you're more in tune with your more emotional (romantic) side! Maybe. At least your desires!

[Anonymous No.12798506]

https://en.wikipedia.org/wiki/Black_hole_electron

Okay, so this says that if an electron was a black hole, it could have all the right properties, but it would be a naked singularity.

Why are we sure that isn't what naked singularities look like?

[Anonymous No.12798543]

how do i calc the uncertainty of theta here?
[math]
\frac{sin(60\pm 0.5)}{1.33sin(35\pm 0.5)} = \theta
[/math]

[Anonymous No.12798565]

>>12798506
Because electrons are completely explained by quantum field theory in every experiment we have performed. GR is a classical theory that can't explain quantum phenomena and most scientists believe that singularities aren't possible in a quantum theory of gravity.

[Anonymous No.12798583]

>>12798543
replace:
60 = x, 0.5 = sigma_x
35 = y, 0.5 = sigma_y
then
sqrt((dTheta/dx)^2 *sigma_x^2 + (dTheta/dy)^2 *sigma_y^2 )
is your uncertainty for a given (x,y)

[Anonymous No.12798593]

Suppose I want to calculate the equations of motion for a perfectly smooth marble rolling around and down a perfectly smooth hyperbolic funnel (with friction) in a vacuum. How many variables do I need to keep track of?

[Anonymous No.12798600]

>>12798583
thanks fren, i should've put that together

[Anonymous No.12798609]

>>12798593
1 parameter for the position and the velocity

[Anonymous No.12798637]

>>12798583
what is [math]d\theta[/math] here though, just the respective value? so [math]d\theta / dx = ???[/math]

[Anonymous No.12798659]

Do free carbon atoms in interstellar space spontaneously polymerize if they meet other free carbon atoms (at negligible relative velocities) without any other elements to interact with? Do they form C[math]_{2}^{+2}[/math], C[math]_{2}^{+4}[/math], C[math]_{2}^{+6}[/math], C[math]_{2}^{+8}[/math] or C[math]_2[/math]?

[Anonymous No.12798668]

>>12798637
sin(x)/1.33*sin(y) is the notation I used
so dtheta/dx = cos(x)/1.33*sin(y)
dtheta/dy = -sin(x)*(cos(y)/sin^2(y)) or whatever

[Anonymous No.12798671]

>>12798543
is this correct?
[math]
\sqrt{(\frac{0.5}{60})^2(0.5)^2 + \frac{0.5}{40}^2(0.5)^2}
[/math]

im not sure, partially because the coefficient in denominator was never used, see
[math]\frac{sin(60\pm 0.5)}{1.33sin(35\pm 0.5)} = \theta[/math]

[Anonymous No.12798682]

>>12798668
oh ok, thanks. pls ignore >>12798671


>or whatever
you're srure though?

[Anonymous No.12798703]

>>12798682
>you're srure though?
Nope
but if no other anon objects we both won't know if it's right or bullshit

[Anonymous No.12798819]

what drugs can I take to hinder my survival instincts from stopping me from killing myself?

[Anonymous No.12798835]

Has the complete schrodinger equation for a single molecule of ground state diatomic hydrogen in a vacuum ever been solved?

[Anonymous No.12798853]

I'm having such a hard time creating standards with a GCMS. My advisor checks in with me once every two weeks and I'm not desperate enough to post on researchgate yet and expose myself as a dumbass. Of course because COVID I'm the only one in the lab and there's no one else here to turn to. welp.

I'm trying to create standard curves for 8 different chemicals around 1ug . My advisor said said just downscale his standards at 1mg to 5mg and then pivoted and said no actually make your own at 1ug (like I originally thought made sense...). My issue is that I run my standards and there is only one peak and they're all at the same time, and have the same spectra as one of the standards. I'm stumped. I have results from my 500 samples in my study that actually make sense but these standards are killing me. I suspect its the GCMS methods but I have no idea how to even begin tampering with that towards what I need.

>tfw new idiot helpless grad student.

[Anonymous No.12798855]

>>12797214
Well energy can be quantified physically... in matter
How can you compare that to the wave function? Where does it become physical?

[Anonymous No.12798871]

Doing basic linear algebra homework.
Might post more than just once (I hope not), but here's one that I'm currently stuck on:
Isn't the only case a 2 x 2 matrix that's all zero? I can't think of anything, when squared by itself, would be a 0 matrix.

[Anonymous No.12798894]

>>12798703
lol

i found htis, still reading it though

https://www.phy.olemiss.edu/lab/englab/weblab/222_Miscellaneous%20folder/222_web_uncertainty_items/Snell_uncertainty_use.pdf

[Anonymous No.12798920]

>>12798894
My cot seems to be alright then

[Anonymous No.12798931]

>>12798871
Those are called nilpotent matrices with index 2, there's a bunch of them.
Example: [math]A = \begin{bmatrix} 0 & 1 \\ 0 & 0\end{bmatrix}[/math]

[Anonymous No.12798936]

It seems like the magic that makes complex analysis tick boils down to the Cauchy Riemann equations. Here's a way to phrase them: Let [math]u,v: \mathbb{R}^2 \to \mathbb{R}[/math] and let [math]f = u + iv[/math]. Then [math]f[/math] is holomorphic iff it's real differentiable, and its derivative, when evaluated at any point, always takes the form
[math]\begin{pmatrix} a & -b \\ b & a \end{pmatrix}[/math]
with [math]a,b \in \mathbb{R}[/math]. Such matrices correspond to multiplication by a complex scalar, i.e. a composition of dilation and rotation.

QUESTION: What if we forget about the structure of [math]\mathbb{C}[/math] and generalize this to [math]n > 1[/math] dimensions? I.e. suppose [math]f: \mathbb{R}^n \to \mathbb{R}^n[/math] is (real) differentiable and assume also that its total derivative takes the above form when evaluated at any point (i.e. [math]\lambda T[/math] where [math]\lambda \in \mathbb{R}[/math] and [math]T[/math] is a rotation in [math]\mathbb{R}^n[/math]). Is there reason to believe that [math]f[/math] is (real) analytic?

[Anonymous No.12798964]

>>12798931
Ohhhhh, that's cool! I'll make sure to mark that in my notes and study that before bed, thank you anon!
Do you know how to do this one? I'm pretty bad with these puzzle-types...

[Anonymous No.12799023]

>>12798964
you can think of that one as being a 4x4 linear system, with each equation being one part of the 2x2 matrix multiplication.

[Anonymous No.12799026]

>>12798964
[eqn]\begin{bmatrix} -9 & -8 \\ 45 & 40\end{bmatrix} \cdot\begin{bmatrix} a & b \\ c & d\end{bmatrix} = \begin{bmatrix} -9a - 8c & -9b - 8d \\ 45a + 40c & 45b + 40d\end{bmatrix} \\ \begin{cases} -9a - 8c = 0 \\ -9b - 8d = 0\\ 45a + 40c = 0 \\ 45b + 40d = 0 \end{cases}[/eqn]

[Anonymous No.12799054]

>>12798964
-9a-8c = 0
-9b-8d = 0
45a+40c = 0
45b + 40d = 0
let b,d = 0
-9a-8c = 0 -> a = -8c/9
let c=1
then a=-8/9
[math]\begin{pmatrix}-9 & -8 \\ 45 & 40\end{pmatrix}\cdot \begin{pmatrix}-8/9 & 0 \\ 1 & 0\end{pmatrix}=\begin{pmatrix}-8+8 & 0 \\ -40+40&0\end{pmatrix}[/math]

[Anonymous No.12799059]

>>12798042
The first S is universally quantified, it says in general subsets of A have the property that there is an element s of A that maps to S. This is just a restatement that S is onto. The S defined on its own line is a specific set, that is where the contradiction comes from. The scheme is suppose that every subset of A has a property, now consider this specific subset, it does not have property, hence the universal statement is false.

[Anonymous No.12799065]

>>12799059
woops
*that f is onto.

[Anonymous No.12799107]

Why don't photons travelling in x direction spontaneously split into two photons travelling at 45° to x direction away from each other?

[Anonymous No.12799136]

>>12799107
conservation of angular momentum I think

[Anonymous No.12799143]

>>12799054
>>12799026
>>12799023
Holy shit I get it now bros. I do the matrix multiplication normally but with variables, and then set those 'cells' equal to the RHS which would be a 2x2 zero matrix, and then solve the 4 systems of equations (along with the free variables) like you guys showed me!
Thanks bros!!!!!!!!

[Anonymous No.12799144]

>>12799136
photons are spin-0

[Anonymous No.12799169]

>>12799144
No, spin 1

[Anonymous No.12799325]

Explain Flip-flops to me like I’m 5 years old. Specifically D and JK flip-flops I’ve been reading definitions of this shit for weeks and still struggle to understand. Why do I need a flip-flop and how do they work? Apparently flip-flops can “hold data values” and they can also be used to stabilize signals? Swell, but out of context, that simply doesn’t mean much to me. It’s worth noting that I’m a total beginner at digital electronics.

[Anonymous No.12799348]

Two questions for this problem:
1) So I have to convert the 3 SoE into their coefficient matrix form and then take the inverse of it, then reduce it to the point where they can then equal the constants? Or do the constants need to be inversed too?
2) Why can I solve a SoE using the inverse and why would I need to do it when I can just do it without the inverse?

[Anonymous No.12799378]

>>12799348
Recall that the matrix form of the SoE looks like [math] Ax = b [/math], where in this case the x vector corresponds to your [x, y, z], and b the RHS of the equation. So taking the inverse of A allows you to manipulate the equation like so: [eqn] Ax = b \implies A^{-1} A x = A^{-1} b \implies x = A^{-1} b [/eqn]. You'll use this method when you're solving larger linear systems not by hand, and understanding how it works is essential for more advanced topics in linear algebra.

>>12798252
Yeah, I'm not gonna pick up an onahole, that's a bit much for me. And the daki is going to completely SFW, so there's even less to be embarrassed about. Just have to get over that initial hump of embarrassment.

[Anonymous No.12799471]

Let's say you had a biodome comprised of two separate layers of glass. Between these two layers contained a barrier of water a few feet thick. Would this layer of water hinder any possible plant growth located within the biodome?

[Anonymous No.12799481]

>>12798920
yeah, python also has an uncertainty library i just learned about, used it to double check

[Anonymous No.12799543]

>>12796332
how the fuck does water work.
like if I dangle the tip of a towel over a bucket of water how does the water defeat gravity and and go up into the towel? Is this a force of the water or the towel?

[Anonymous No.12799557]

Any idea how can I add .sh to bash/Borne files that are found with other different files?

I'm forced to use File command to find which ones are bash then rename them.

I tried

file folder/* | grep 'Bourne'
But obviously I can't rename that output.

I was told Xargs is could be useful too.

[Anonymous No.12799581]

can I say that for every function [math]\mathbb R \rightarrow \mathbb R[/math] you can just apply your variables and solve directly?

[Anonymous No.12799590]

>>12799581
I'm talking about limits btw. not sure why I didn't mention it

[Anonymous No.12799618]

>>12799378
>So taking the inverse of A allows you to manipulate the equation like so:
Ohh, I get it now! It makes a lot more sense seeing your manipulation visually, thank you anon! My brain is full of knowledge now

[Anonymous No.12799621]

>>12799325
logisim also flip flop and latch etc. are used interchangeably by boomers for job security

[Anonymous No.12799622]

>>12799543
It’s pretty much just capillary force overcoming gravity.

[Anonymous No.12799645]

>>12799378
>Yeah, I'm not gonna pick up an onahole
>that's a bit much for me
>And the daki is going to completely SFW, so there's even less to be embarrassed about
>Just have to get over that initial hump of embarrassment
That's why I said 'anytime soon' senpai :^)
Jokes aside-- nevermind, I can't find a way to write you a proper reason without sounding like a massive degenerate, maybe I already do sound like one.
>SFW
Based... Just make sure that you don't hold yourself back when giving your artist/commission guy your nitpicks because you'll be sleeping with her for a very long time!

[Anonymous No.12799658]

>>12799325
well, you can get an intuitive notion just by looking at their physical implementation. all you need is to know how AND, OR and NOT gates work. then you can set J and K values in your mind and see how the circuit behaves for each of them every clock pulse. for latches just ignore the clock signal.

[Anonymous No.12799674]

>>12799325
>I’ve been reading definitions of this shit for weeks and still struggle to understand.
For you to properly understand D and JK flipflops, you need to understand what the SR latch does as both of them incorporate an SR latch which does the 'data holding.' And to properly understand a SR latch, you have to write down its equations and then plug in values of the 4 binary states that it can be in and you'll see why they can hold their values.

https://www.youtube.com/watch?v=iEs69UUHLNw&ab_channel=ZahiHaddad

Longer video but since you've spent weeks on it, you should be able to be willing to spend an hour on this video right?

See pic related for what I mean by SR latch equations.

[Anonymous No.12799687]

can someone give me a quick rundown on
>neuro-pharmagology of endorphines
WHY do they make us feel good,how are they produced/manipulated?

[Anonymous No.12799763]

>>12799581
>>12799590
what does "apply your variables" mean

[Anonymous No.12799795]

Doing some true or false questions and I came across this one:
Why is this one false? I've been trying to wrap my head around it for a while. Assuming that the person doing the row operation did it perfectly and it results in an inconsistent system, wouldn't that just mean that the original system was inconsistent, to begin with because he couldn't find an answer?
The solution manual said false because:
1 0 | 1
0 1 | 0
0 0 | 0
but didn't say any more than just that.

[Anonymous No.12799890]

>>12799622
just is a thought experiment, could you dangle a long towel from a plane and get water up to it with no power source?

[Anonymous No.12799893]

For about 10 years now I have created an elaborate alternate sci-if universe that I build while going to sleep. What mental disease is this?

[Anonymous No.12799906]

>>12799107
conservations of spin, quantum number whatever
another way to think about it is that photons don't interact with each other: a photon decay is just the opposite of two photons merging. since they don't interact, neither is possible

[Anonymous No.12799927]

>>12798079
Email the author and get the solutions notes for the exercises. He mails them directly from Vermont. That material is extremely helpful and explains the solutions flawlessly.

[Anonymous No.12799973]

>>12799763
i mean substituting x for a in [math]\lim_{x \to a} f(x)[/math] and solve it as the actual f(a)

[Anonymous No.12799997]

>>12799973
No. If f(x) has a discontinuity at a, then [math] \lim_{x \to a} f(x) [/math] either DNE or =/= f(a).

[Anonymous No.12800031]

Alright one last question BC I'm about to throw up from exhaustion.

Command find -exec -perm

I need to give the same permissions (rwx) that 'others' have to 'group'.
I already found the files in which 'others' have the rights that 'group' doesn't have.

I did: find folder -perm /o=rwx.

Cheerio.

[Anonymous No.12800043]

>>12799893
It's called write a sci fi book

[Anonymous No.12800053]

>>12799997
true, thank you

[Anonymous No.12800063]

>>12799795
what is
1 0 | 1
0 1 | 0
0 0 | 0
even? a 2x3 matrix or three 1x2 matrices?

[Anonymous No.12800068]

>>12800063
3x2*
also what does the | operator mean

[Anonymous No.12800145]

Why?:

123456789=
(1+2) 3 (4+5) 6 (7+8) 9
=3 =9 =15 (1+5) = 6

[Anonymous No.12800190]

>>12800068
Oh my bad, the left is the coefficient and the right is the constant, I tried to imitate how the matrix kind of looks

[Anonymous No.12800231]

If electrons move through a wire at 1 millimeter a second then why do I not die when I turn a switch off then touch the wire?

[Anonymous No.12800232]

>>12796332
Can someone please help with this question?

Let [math]\alpha \in \mathbb{R}[/math] and [math]w \in \mathbb{C}[/math]. For [math]z \in \mathbb{C}\H_{\alpha}[/math] we define de [math]w[/math] power of [math]z[/math] as
[eqn]P_{\alpha}^w (z) = e^{w \log_{\alpha} (z)[/eqn]
Now consider [math]f(z) = P_0^{1/3}(z)[/math].\
(1) Find its definition domain [math]A[/math] and the image set [math]B = f(A)[/math]
(2) Let [math]g(z) = z^3[/math] Find out if for all [math]z \in A[/math] it holds that [math]g(f(z)) = z[/math]
(3) Find out if for all [math]z \in B[/math] it holds that [math]f(g(z)) = z[/math] What about for all [math]z \in \mathbb{C}[/math]

Im guessing the domain is [math]\mathbb{C}\H_{\alpha}[/math] but I dont know how to attack the rest

[Anonymous No.12800234]

>>12796332
What is the best suicide? Self immolation looks cool but there's also chemical gases or heights. Idk, which is the coolest?

[Anonymous No.12800236]

>>12796413
An assberg

[Anonymous No.12800237]

>>12800232
fucking hell

[eqn]P_{\alpha}^w (z) = e^{w \log_{\alpha}} (z)[/eqn]

[Anonymous No.12800254]

>>12800190
I still dunno what you mean but I just started Linear Algebra in school so it's probably on me. but here's what I found: https://www.slader.com/discussion/question/in-each-case-either-show-that-the-statement/
letter c) is similar to you question and it is true. I dunno how it could be false. maybe it's an error by the author?

[Anonymous No.12800259]

>>12800231
Why would you die?

[Anonymous No.12800284]

>>12800068
| is shorthand for augmentation or equality, so the first row would be 1x + 0y = 1, or whatever your variables are in place of x,y.

[Anonymous No.12800355]

>>12800284
gotcha, so left is 1 and right is 0, correct? I'm still confused as to how this answers anon's question though. why is it false?

[Learnfag No.12800373]

On F𝖆ctoring Th𝖊 Sum 𝖆nd Diff𝖊r𝖊nc𝖊s of Pow𝖊rs

I have a couple of questions related to the title of this post (1st line).
First, is there a general way to factor [math]a^n+b^n[/math]? I believe I've seen one for when [math]n[/math] is odd but none for when [math]n[/math] is even, why?
How do you prove: [eqn]\begin{split}
a^n-b^n &= \sum_{j=0}^{n-1}a^{n-j-1}b^{j}\\
&= (a-b)(a^{n-1}+a^{n-2}b+a^{n-3}b^2+...+a^{2}b^{n-3}+ab^{n-2}+b^{n-1})
\end{split}
[/eqn]
I got filtered by proof wiki
Finally, why do people separate [math]a^n-b^n[/math] into two different equations for odd and even [math]n[/math]s?

[Anonymous No.12800429]

>>12800355
i didn't read the parent question until now, i don't understand how it's false either.

but
1 0 | 1
0 1 | 0
0 0 | 0

this would just represent the following equations
1x + 0y = 1
0x + 1y = 0
0x + 0y = 0

clearly y=0 and x=1, i don't see any inconsistency going on and would say the quote in the picture provided was true, i.e if row operations expose an inconsistent system, the system was inconsistent. but maybe im misunderstanding or something

[Anonymous No.12800530]

>>12800259
If its 480 when the switch is closed, then it's still apparently full of electrons when I open the switch, why do I not die?

[Anonymous No.12800662]

Ok, I know the answer, thanks Wolfram, but I don't see how.

I begin with
[math]
\int_0^1 e^{-st}tdt + \int_1^{\infty} e^{-st}
[/math]

which is easy enough to integrate with a calculator, but my ansewr doesn't align with Wolframs of [math]\frac{1-e^{-s}}{s^2}[/math]

another answer is here:
>https://www.slader.com/textbook/9780321796981-differential-equations-and-boundary-value-problems-computing-and-modeling-5th-edition/482/problems/20/#

but im not so slick on the theory yet

[Anonymous No.12800754]

>>12796332
Brainlet here. How do I know when to use the different equations for gibbs free energy?
I only know that ΔG°=ΔH°-TΔS° is used when a reaction is at a standard state, being 1 atm.
What about ΔG=ΔG°+RTlnQ or ΔG°=-RTlnK? Does it just depend on what variables are given to me?

[Anonymous No.12800776]

>>12800662
That's a funky hint. I'd instead represent that signal as [math] f(t) = u(t)t - u(t-1)(t-1) [/math]. Then you can just use your transform tables and the time-delay property to see that [math] F(s) = \frac{1}{s^2} - \frac{e^{-s}}{s^2} [/math].

[Anonymous No.12800794]

>>12799325
>Flip-flops
same as latches, except driven by a clock
surprisingly, this changes the function
https://youtu.be/YW-_GkUguMM

[Anonymous No.12800985]

>>12800662
> but my ansewr doesn't align with Wolframs
Are you sure you don't just need to rearrange?
[eqn]\int_0^1 e^{-st}t \, dt = \left . {-(1+st)e^{-st} \over s^2} \right \vert_0^1 = {-(1+s)e^{-s} \over s^2} - {-1 \over s^2} = {1-(1+s)e^{-s} \over s^2}[/eqn]
[eqn]\int_1^\infty e^{-st} = \left . -{e^{-st} \over s} \right \vert _1^\infty = 0 - \left( -{e^{-s} \over s} \right) = {e^{-s} \over s}[/eqn]
[eqn]\begin{align} & {1-(1+s)e^{-s} \over s^2} + {e^{-s} \over s} \\ = & {1-(1+s)e^{-s}+se^{-s} \over s^2} \\ = & {1-e^{-s} \over s^2} \end{align}[/eqn]

But as >>12800776 says, you're probably supposed to use the time-shift property f(t-a)u(t-a)=e^(-as)F(s). The function is f(t)=g(t)-g(t-1) where g(t)=u(t)t.

[Anonymous No.12801204]

>>12800662
>>12800776
Wtf, can someone explain how that hint even works?
What's u(t)?

[Anonymous No.12801637]

>>12799927
i already have the solutions manual, i'm not that great at maths and i know i wouldn't get far without it, but thanks for the tip anyway!

[Anonymous No.12801660]

>>12801637
Don't worry, keep trying and post your questions here. Many here are able to help you.

[Anonymous No.12801699]

>>12801204
> What's u(t)?
The Heaviside step function:
[eqn]u(x) = \begin{cases} 0 & x<0 \\ 1 & x \ge 0 \end{cases}[/eqn]
The Laplace transform is usually given for the product of a function with u(t), forcing the expression to be zero for t<0. E.g. L{t.u(t)}=1/s^2.

For the bilateral Laplace transform (where the integral is over [-∞,∞]), omitting the u(t) often causes the integral to diverge because e^-st->∞ as t->-∞. For the one-sided Laplace transform (where the integral is over [0,∞]), multiplying by u(t) doesn't make any difference because u(t)=1 over the range of integration. But it's often left in to clarify that the transform only depends upon the behaviour of the function for t>=0.

It's important to note in this case that e^(-as)F(s) is the Laplace transform of u(t-a)f(t-a), not of u(t)f(t-a). I.e. when you delay by 1 second, you get a function which is zero for the first second then starts increasing from zero at t=1, not a function which starts at -1 at t=0.

[Anonymous No.12801702]

>>12801699
>Heaviside
Oh, never seen that notation used before

[Anonymous No.12801714]

>>12801699
> the time-shift property f(t-a)u(t-a)=e^(-as)F(s).
That could have been worded better.
L{f(t-a)u(t-a)}=e^(-as)F(s)

>>12801204
> can someone explain how that hint even works?
f(t)=(u(t)-u1(t))t-u1(t)
= (u(t) - u(t-1))t - u(t-1)
= u(t)t - u(t-1)t - u(t-1)
= u(t)t - u(t-1)(t-1)

L{u(t).t}=1/s^2 (standard transform)
L{u(t-1)(t-1)}=e^(-s)(1/s^2) (time-shift property, a=1)
L{u(t).t-u(t-1)(t-1)} = L{u(t).t}-L{u(t-1)(t-1)}
= 1/s^2-e^(-s)/s^2
= (1-e^(-s))/s^2

[Anonymous No.12801796]

>>12796332
why is colour represented with hexadecimal?

[Anonymous No.12801819]

Good literature to understand quaternions?

> background
Retarded cs undergrad

[Anonymous No.12801826]

-2x^-1/2 * e^-4x1/2
and
sqrt(2e^-2sqrt(2x))/sqrt(x)

Are these identical?

[Anonymous No.12801831]

>>12801826
put that in latex so we can read it correctly.

[Anonymous No.12801833]

>>12801831
Last time I did that it showed up wrongly, I feel like I'm missing something
[math]
-2x^-1/2 * e^-4x1/2

sqrt(2e^-2sqrt(2x))/sqrt(x)
[/math]

[Anonymous No.12801840]

>>12801833
bruh. that's still unreadable.

[Anonymous No.12801856]

>>12801840
Ok how about this. Are these the same?

[Anonymous No.12801871]

>>12801856
No

[Anonymous No.12801887]

>>12801871
Where's the error?

[Anonymous No.12801905]

>>12801856
>>12801887
are you dyslexic? that's even harder to read and makes no sense.

[Anonymous No.12801910]

>>12801887
2*sqrt(2) != 4
And whatever you did in the fourth line

[Anonymous No.12801920]

>>12801699
Bold of engineers to just go and use fucking u for a specific function.

[Anonymous No.12801998]

>>12801920
Eh. In controls you instead use [math] 1(t) [/math] for the unit step, since [math] u(t) [/math] typically indicates the control signal (i.e. the output of your controller, which goes into your plant as input) and you usually assume that your signal is 0 for t < 0 anyways.

[Anonymous No.12802005]

>>12801998
Why not just use theta like the rest of humanity

[Anonymous No.12802025]

>>12799890
No.

[Anonymous No.12802047]

>>12800530
That's not how electricity works. Energy in an ideal wire is not stored. electrons are everywhere, but if there is not a electric field present, then there is no motive for these electrons to move

[Anonymous No.12802049]

>>12801887
Hard to read; but one thing to note is that e^(ab) ≠ (e^a)(e^b)

[Anonymous No.12802050]

>>12801796
It's not always. It can be a decimal too

[Anonymous No.12802060]

>>12801920
We still use it, unlike you, we can use whatever notation we want. Y'all's relationship ended years ago, anon. Move on

[Anonymous No.12802063]

>>12802005
Never seen theta for the unit step. Who uses that notation?

[Anonymous No.12802065]

>>12802060
>we can use whatever notation we want
Yes because nobody reads it

[Anonymous No.12802071]

>>12801887
I hope you're trolling

[Anonymous No.12802074]

>>12802065
Not him, but using [math]u,v,\theta[/math] as notation for functions is ubiquitous in advanced analysis and probability

[Anonymous No.12802075]

>>12802063
https://functions.wolfram.com/GeneralizedFunctions/UnitStep/
Almost every physics book I've read used theta or sometimes H

[Anonymous No.12802077]

>>12802074
I know, that's why using it for H is stupid

[Anonymous No.12802081]

>>12802075
Interesting, I've seen H sparingly before from non EEs (h / H is typically the impulse / frequency response or transfer function) but not theta. How do you typically indicate things like angles then? phi? Or do unit steps not come up when you usually care about the angles between things such as with collisions?

[Anonymous No.12802086]

>>12802077
[math]H[/math] isn't a good notation imho. Capital Latin letters should be reserved for sets or linear operators depending on the context. The best notation for heaviside is [math]\mathbb{I}_{[0, \infty)}(x)[/math] which is clear and compatible with the theory of integration.

[Anonymous No.12802098]

>>12802081
Just any greek letter that's not in use.

[Anonymous No.12802119]

Why do men piss and cum from the same hole but women have both a vagina and an urethra?

[Anonymous No.12802121]

>>12802086
That's not notation, you're just writing out the entire definition.
Although using [math]\mathbb{I}[/math] instead of just [math]\chi[/math] for indicator functions is weird.

[Anonymous No.12802129]

>>12802119
Urine and semen are both liquids, so they can exit the body through the same path. On the other hand, a fully formed baby is not a liquid.

[Anonymous No.12802145]

>>12802121
you clearly haven't seen much if you say that [math]\mathbb{I}[/math] is 'weird'

[Anonymous No.12802373]

Suppose I know that a polynomial [math]x^5+3x^4y+5x^3y^2+5x^2y^3+3xy^4+y^5[/math] is divisible by (x+y). Is there a quick way to get the quotient or performing a long (synthetic) division is the best way to do it? By 'quick way' I mean something that can be done without paper.

[Anonymous No.12802406]

x^2+x=0
One solution is x=0, why can you still divide by x?

[Anonymous No.12802418]

>>12802406
Because dividing by x yields a nonzero solution

[Anonymous No.12802434]

>>12802406
Formally we have that
[math] y=\frac{x(x+1)}{x}[/math]
is [math]y:\mathbb{R}/\{0\} \to \mathbb{R}[/math] so it is a 'different' function from [math]z=x+1[/math] which is [math]z:\mathbb{R} \to \mathbb{R}[/math] but [math]\lim_{x to 0}y=1[/math] so we can 'fill in' y at 0 by forcing its value at 0 and we basically get z

[Anonymous No.12802442]

I understand the mechanic of diagonolization argument, but I can't quite understand how it can give direct proofs (by contradiction).

[Anonymous No.12802453]

>>12802442
Diagonalization shows that there exists an element that is simply not present in the 'table' by construction, but should be, which creates a contradiction. If we assume the set [math][0,1][/math] is countable, we show that by claiming it is countable we leave out an element which actually should be there, but it isn't, so the set is not countable.

[Anonymous No.12802463]

>>12802442
diagonalization argument DIRECTLY proves the following statement: for any list of real numbers indexed by natural numbers there exists a real number not on the list.

[Anonymous No.12802465]

Anyone have that one picture comparing actual scientists commenting on God and then those modern popsci fags throwing the whole concept out the window?

[Anonymous No.12802484]

I realized I should've asked this question a long time ago but I didn't for some dumb reason.

How do you guys study something you're not interested in (but are forced to by the curriculum)?

[Anonymous No.12802499]

>>12802484
By speed running it immediately so it's out of mind, out of daily order, out of sight.

[Anonymous No.12802516]

>>12802484
If I don't like the subject, I simply treat the exam as a challenge/game that I have to excel at. It's called 'exam oriented mindset'. It is extremely toxic because you will learn to game exams and not the material so I don't recommend doing it. However, it is very effective if you have good memory and identify all tricks the prof may throw at you. It's a you vs prof game. Most people who graduate with stellar GPAs have this mindset and that's why many of them don't remember much of the material. I passed some exams with 100% with this strategy but I couldn't recall one thing the day after the exam.

[Anonymous No.12802535]

>>12802516
I have such a shit fucking memory. I can remember the page number where I can have the asked information, the entire picture of the page structure in my mind, but can't 'see' the text. It's why I have to pre-study on my own for everything. Reading before exams never did anything to help me.

[Anonymous No.12802537]

>>12802406
> One solution is x=0, why can you still divide by x?
Because x isn't *necessarily* zero. Formally, if you divide by x you get
x+1=0 | x≠0
But to say that the qualification (x≠0) is superfluous would probably be an understatement.

[Anonymous No.12802587]

This is probably stupid but its why im here
I cannot get my head around this module, every question I get I have no idea where to start.
Please can someone push me in the right direction with this one

[Anonymous No.12802604]

>>12802535
You have to make up a study method. For me, it is effective to list all topics and subtopics in dense lists in one-two sheets of paper (written on by hand). Then for every topic and subtopic in the list I define a satisfactory answer (Either in my mind or written) for anything that can be thrown at me. So when recalling information, I 'see' the list in my head, and to every element I associated some answers that I memorized. I find memorizing the words of others very hard so I don't try to recall the exact words I saw in on a page, I just recall a list of topics and a number of info that I comstructed branching from such list.

[Anonymous No.12802641]

Do all particle annihilation events have to produce multiple photons? Why can't they make exactly one photon?

[Anonymous No.12802675]

>>12802373
Generalisation of Pascal's triangle

(x+y)(c0.x^4+c1.x^3.y+c2.x^2.y^2+c3.x.y^3+c4.y^4)
= c0.x^5+(c0+c1).x^4.y+(c1+c2).x^3.y^2+(c2+c3).x^2.y^3+(c3+c4).x.y^4+c4.y^5

So c0=1, c0+c1=3, c1+c2=5, c2+c3=5, c3+c4=3, c4=1
=> c1=2, c1+c2=5, c2+c3=5, c3=2
=> c2=3
IOW, working from the outside in, copy the first coefficient, then subtract the current coefficient from the next coefficient in the dividend to get the next coefficient in the quotient.
1,3,5,5,3,1 => 1,2,3,2,1
If you get different values for the middle coefficient, it wasn't actually divisible by (x+y).

[Anonymous No.12802689]

>>12802587
Maybe this one can be useful. In the first part, define the sets
[math]A^n_k:=\{b^{(k-1)/n}\leq x < b^{k/n}\}[/math]
and
[math]f^n_k(x)=
\begin{cases}
b^{c(k-1)/n}, x \in A^n_k \\
0, x \notin A^n_k
\end{cases}
[/math]
and the sequence
[math]h_n(x)=\sum_{k=1}^nf_n(x)[/math]

[Anonymous No.12802700]

>>12802689
*
[math]h_n(x)=\sum_{k=1}^n f^n_k(x)[/math]

[Anonymous No.12802738]

>>12802465
please

[Anonymous No.12802748]

How would you solve congruences like these:
x^2+1≡0 mod 13^3
x^3-2x^2-7x+3≡0 mod 7^2

[Anonymous No.12802750]

>>12802738

[Anonymous No.12802751]

>>12802750
thanks

[Anonymous No.12802760]

>>12802751
It's not about God but I think this is what you were looking for

[Anonymous No.12802770]

>>12802760
it is

[Anonymous No.12802772]

>>12802689
thanks
I had already done something similar but I dont know where to go from there, as in how to prove it converges uniformly to f(x)

[Anonymous No.12802789]

>>12802675
Thank you. I think this is something that I wanted to hear. I could reason that since we can generate n-th row of pascal's triangle with (x+y)^n, then proceeding to the next row is just multiplying by (x+y), so the coefficients of a multiplied polynomial is of the form you've written. This association is exactly what I wanted.

[Anonymous No.12802797]

>>12802772
I'm on mobile and cant write so I can only go so far. Basically check that the difference between the function and the sequence (in one of the disjoint sets we defined) is less than a term that decreases as n goes to infinity. Then check that all the differences in all the sets we defined can be made less than a term dependent on n. If this is the case, you prove uniform convergence. For the integral, sum up the rectangles created by that segmented function and see if it converges to the right value.

[Anonymous No.12802799]

Is this question answerable with only the information provided?

[Anonymous No.12802802]

>>12802797
tysm :)))

[Anonymous No.12802850]

>>12802797
Something like
[math]|x^c-b^{c(k-1)/n}|\leq |b^{c(k)/n}-b^{c(k-1)/n}|=b^{ck/n}|1-b^{-c/n}|<b^{ck/n}<b^{c/n}[/math]
Check if this makes sense, but I think this is the general approach you need

[Anonymous No.12802855]

>>12802799
yes

[Anonymous No.12802868]

>>12802855
Alright, thank you.
With that being the case, following the principle that current follows the path of least resistance, it will just involve R3 and R4, correct?

[Anonymous No.12802874]

I've been doing citizen science under lockdown and my work is starting to yield some results. I've been documenting my work extensively and I've starting writing an article documenting my findings. I'd rather not say what I'm working on because it's pretty specific and I could be traced back to 4chan, which isn't a good look in a highly professional field like hard science.
Here's the question: I have 0 experience with publishing scientific articles. Once my work is edited/spellchecked/bibliographed etc. and it's ready to appear in front of the eyes of others, who/what/where do I send it? Do I just look up a variety of publishers and send it to their e-mail address? Is there a specific department I need to talk to? Pls halp.

[Anonymous No.12802881]

With all of the additives in food, how come food related deaths aren't extremely common? Surely someone by now has died of eating the worst possible combination of food and exploded in a violent chemical reaction or died of some neurotoxin released in their stomach?

Is it because there's not enough of it to make enough of something to be harmful to humans, or do they seriously test everything against everything to make sure it doesn't blow up?

[Anonymous No.12802882]

IDK if this should go here or in/mg/ but this place has more IPs so whatever. I've been trying to solve a problem where I know it should be easy but I can't seem to word it right.

If [math] X [/math] is Hausdorff and has a compact universal cover, then [math] \pi_1(X) [/math] is finite.

I'm pretty sure I'm on the right track in trying to pull a contradiction by considering the fibers and maybe somehow there exists a cover with no finite subcover, but idk how to cement that logic. Is there an easier way?

[Anonymous No.12802899]

>>12802881
what the fuck do you think the FDA spends all fucking day doing?

[Anonymous No.12802906]

>>12802899
Eating burgers and shooting people, I don't know, I'm not American

[Anonymous No.12802921]

>>12802855
>>12802868
nevermind I see what's going on. I forgot you could "deactivate" independent sources in circuits without dependent sources, in order to derive the thevenin resistance.

[Anonymous No.12803002]

>>12800063
>>12800068
>>12800190
>>12800254
>>12800284
>>12800355
>>12800429
Turned out the solution manual was fucking bollocks. Had to email the professor and he says it's true too.

[Anonymous No.12803014]

>>12800985
thanks, i did just need to rearrange and messed up the algebra on the integration somewhere as well

>>12800776
i thought it was really funky too, thanks for the help goys

[Anonymous No.12803028]

Anyone else thinks that some matrix problems are unnecessarily long? I'm just starting to learn it but some of these questions take pages of row operations and involves fractions, why do professors want you to go through this mess manually when we've practiced a bunch already?

[Anonymous No.12803128]

My cell cultures keep getting contaminated. I'm working at home and not in a proper lab. Are there any specific tips so I can prevent this in the future?

[Anonymous No.12803205]

So I'm supposed to express y as a linear combination of a1, a2, and a3, or show that it is not. I still don't understand what exactly does it mean for something to be a 'linear combination' of something else.
My current idea is that I create a matrix of a1, a2, a3, and then add in y as the 4th column and then see if it equals zero, like Ax = 0 except x is the y vector. Is this how I'm supposed to do it?

[Anonymous No.12803254]

>>12803205
linear combination of x=(x1,x2,x3) is a*x1+b*x2+c*x3 for constants a,b,c
In your case it would be
a*(-1)+b*3+c*1=-1
a*3+b*1+c*1=9
etc.
Is it possible to write it like that? It's a linear combination.

[Anonymous No.12803265]

>>12803254
Ohhhh, so it's asking whether or not the RREF/REF of the augmented matrix of all of those 4 vectors will result in an answer/be consistent? Okay, I think I get it now, thank you!

[Anonymous No.12803268]

>>12803205
A vector y is considered to be a linear combination of some other set of vectors if there exist scalars x1, x2, etc. s.t. y = x1a1 + x2a2 +... The conceptual way to think of it is that y lies in the space spanned by your vectors a1 through an. So for example, if our vectors are [math] \hat{x}, \hat{y} [/math], we can express any vector in the xy plane as a linear combination of [math] \hat{x}, \hat{y} [/math] (coefficients given by the vectors x and y components), but not any vectors with a z component since no combination of [math] \hat{x}, \hat{y} [/math] can give a z component.

You're close for how you want to set up your problem, but not quite. You do want to setup an A matrix like you've described, but instead you want to find some vector x such that Ax = y, where each element of x corresponds to the coefficient of each a_n. Note that your setup doesn't actually make sense in this case, since y is 4x1 elements, but A is a 4x3.

[Anonymous No.12803272]

>>12803205
>I still don't understand what exactly does it mean for something to be a 'linear combination' of something else.
To show that y is a linear combination of a1, a2, a3, you'd need to find scalars [math]\lambda_1, \lambda_2, \lambda_3[/math] such as[math]y = \lambda_1 a_1 + \lambda_2 a_2 + \lambda_3 a_3[/math]
What you can do is show whether the system
[eqn]\begin{cases}
-\lambda_1 + 3\lambda_2 + \lambda_3 = -1 \\
3\lambda_1 + \lambda_2 + \lambda_3 = 9 \\
2 \lambda_2 + \lambda_3 = 2 \\
\lambda_1 + \lambda_3 = 6 \end{cases}[/eqn]
can be solved or not. This is equivalent to solving [math]Ax = y[/math], where [math]x = \begin{pmatrix} \lambda_1 \\ \lambda_2 \\ \lambda_3\end{pmatrix}[/math], and A is a 4x3 matrix where the columns are a1, a2, a3.

[Anonymous No.12803277]

Can anyone help with the convergence radius on this one?
[latex]
\sum_{n=1}^{\infty} \frac{n!}{3 \cdot 6 \cdot 9 \cdot \dot \dot 3n} x^n
[latex]

[Anonymous No.12803282]

>>12803277
fuck

[latex]
\sum_{n=1}^{\infty} \frac{n!}{3 \cdot 6 \cdot 9 \cdot \dot \dot 3n} x^n
[/latex]

[Anonymous No.12803285]

>>12803282
it's [ math][ /math] without the whitespace

[Anonymous No.12803287]

>>12803277
>>12803282
Forgot that it is math.
[math]
\sum_{n=1}^{\infty} \frac{n!}{3 \cdot 6 \cdot 9 \cdot \dot \dot 3n} x^n
[/math]

[Anonymous No.12803291]

>>12803277
>>12803282
>>12803287

[Anonymous No.12803292]

>>12803287
anon-kun, click the tex button at the top left of the reply window to preview

[Anonymous No.12803293]

>>12803285
>>12803287
Just fuck my shit up

[Anonymous No.12803298]

>>12803293
You can still delete and hide your shame onii-chan

[Anonymous No.12803299]

>>12802129
That makes sense, thanks.

[Anonymous No.12803303]

>>12803287
Did you mean
[eqn]\sum_{n=1}^{\infty} \frac{n!}{3 \times 6 \times 9 \times \cdot \cdot \cdot \times 3n} x^n[/eqn]

[Anonymous No.12803306]

>>12803298
I wont, the shame is part of the lesson.

[Anonymous No.12803312]

>>12803306
That's right onii-chan, you just have to keep moving forward

[Anonymous No.12803313]

>>12803303
Yes, thank you.

[Anonymous No.12803319]

>>12803313

[math]3 \times 6 \times 9 \times \cdots \times 3n = 3^n(1 \times 2 \times 3 \times \cdots \times n)[/math], taking out [math]n[/math] factors of [math]3[/math].

[Anonymous No.12803320]

>>12803313
The bottom part is just [math]3^n n![/math], which means your series is simply
[eqn]\sum_{n=1}^{\infty} \frac{x^n}{3^n}[/eqn]
which makes the radius fairly obvious

[Anonymous No.12803323]

>>12802882
First of all, look at the wikipedia definition because I'll use the letters from there.
Look at your [math]U[/math], and consider now the set of all of its images under deck transformations (which are all disjoint). If the group of deck transformations is infinite, that's an infinite number of disjoint open sets. You can then use that and Hausdorfness to derive the contradiction.

[Anonymous No.12803332]

Can you guys not recommend me going to /an/ to grab pictures to post questions with? Every time I go, I spend at least 20 minutes there.

[Anonymous No.12803342]

>>12803320
>>12803319
I see, thank you all for all your help and kindness.

[Anonymous No.12803458]

This thread went really fast.
>>12803332
It's the only reasonable option.
>attach a picture of a 3D woman
>>this fucking coomer
>attach a picture of an anime girl
>>this fucking tranny
>attach a shitty meme
>>this fucking redditor
>attach a picture of food
>>this FAT PIECE OF SHIT
>attach an in-topic picture
>people start discussing it
etc etc.

[Anonymous No.12803470]

>>12803268
>Ax = y
Ahh, fuck. I was close though! I get really confused whenever they word questions like this rather than just giving you a matrix and going "ok see if it is consistent."
>Note that your setup doesn't actually make sense in this case, since y is 4x1 elements, but A is a 4x3.
Oops... Good point, I'll note that down, would be an easy way to catch a potential error in the future. Thank you anon.
>>12803272
>This is equivalent to solving Ax=y
>Bunch of LaTex stuff
Thank you for writing it out anon, it's a lot clearer seeing it, I have to start learning how to write in it so that I don't look like a primate.

[Anonymous No.12803485]

>>12803470
Oh, I forgot to ask this short question:

If you have a free variable (or more than one) when trying to see if something is a linear combination of a set of vectors, does that mean that it's still a linear combination?

[Anonymous No.12803529]

>>12803485
Yup! Just means that there are infinitely many valid combinations, which indicates that one of your vectors is probably unnecessary.

[Anonymous No.12803539]

>>12803529
>which indicates that one of your vectors is probably unnecessary.
And those vectors are the ones that produce a free variable right? Thank you anon, solidifying knowledge every day...

[Anonymous No.12803559]

>>12803539
Exactly! You can tell since setting the free variable to 0 essentially gets rid of that vector from your linear combination.

[Anonymous No.12803592]

>>12803559
>setting the free variable to 0 essentially gets rid of that vector
Right, I just remembered I could literally plug in zero for the free variables. Thank you again anon!

[Anonymous No.12804386]

Any baby differential equation textbook I can learn from? Around the 'level' of James Stewart / Anton?

[Anonymous No.12804406]

I asked this in the other thread about this but no one answered. I'm trying to find an example of two maps [math] f: A\to B, p: E\to B[/math] where f is a homotopy equivalence such that the pullback [math] \pi_E: E\times_BA\to E[/math] is not a homotopy equivalence. I was thinking that I should let [math] f:A\to B[/math] be a homotopy equivalence between non-contractible spaces and then p be some map that forces the projection to be not a homotopy equivalence.

[Anonymous No.12804486]

any idea what I'm really being asked in the second problem?

>>12804406
I'm reading the one by Edwards and Penney, really like it actually and if you like Stewart it'll be right up your corn-hole.

[Anonymous No.12804504]

>>12804486
The equilibrium point is the (x,y) such that neither x nor y is changing, i.e. the time derivative of x and the time derivative of y are both 0.

[Anonymous No.12804518]

>>12804486
Anon I think you might've replied to the wrong person

[Anonymous No.12804530]

>>12804504
right, so would I just have something like
[math]
(\alpha - \beta y) = 0, \delta x - \gamma = 0
[/math]

? or do I need to solve for x, then sub x for y,... just not sure how to continue (...and don't quite feel like re-reading...)


>>12804518
oops, thx, meant for >>12804386

[Anonymous No.12804554]

>>12804530
Since x & y are assumed to be nonzero, it's fine to divide through like that. There's not really much else to the problem - find your x & y from those two simple equations, maybe double check your answer by plugging back in, that's it.

[Anonymous No.12804563]

>>12804406
Consider [math]A = S^1[/math], [math]E = B = \mathbb{R^2}[/math]. The maps are the inclusion and the identity.
Then the pullback is just [math]S^1[/math] again, and it's not homotopy equivalent to R^2.

[Anonymous No.12804568]

>>12798835
analytically? no
numerically? yes

[Anonymous No.12804590]

i’m currently about to finish my bachelor of science, with a major in pure mathematics, and i’m beginning to realise that i’m probably not smart enough to do a phd in math
how difficult would it be to switch over to getting a phd in computer science, with the eventual hope of getting into a tenure position?
everyone makes fun of cs grads here but it seems like an easier way to get into academia, or at least an easy way to get a high paying comfy industry job

[Anonymous No.12804594]

>>12804554
so is that my answer, what I typed above? i.e
[math]
(\alpha - \beta y) = 0, \delta x - \gamma = 0
[/math]

or do I need to do something like:
[math]
\alpha - \beta y = \delta x - \gamma
\rightarrow x = \frac{(\alpha - \beta y + \gamma)}{\delta}
[/math]
then use x to solve for y and.... ?

please excuse my room temp iq and lack of effort today

[Anonymous No.12804597]

If the double slit experiment doesn't work after first measuring the particle, then how long does it take for the particle to "reset"?

[Anonymous No.12804622]

>>12804594
You just need to take those two equations, [math] \alpha - \beta y = 0 [/math] and [math] \delta x - \gamma = 0 [/math], and then solve for y in terms of alpha & beta using the first equation, and x in terms of gamma and delta using the second. Don't overthink it!

[Anonymous No.12804660]

>>12804622
thanks fren

[Anonymous No.12804677]

>two particles collide
>they entangle
>two particles collide
>they decohere
which one is it then?

[Anonymous No.12804720]

>all the forks are in the dishwasher so you eat cake with the knife you used to cut it
>you finish the slice and still want more, so you dirty another knife afterwards to serve yourself more

[Anonymous No.12804896]

>>12804720
Honey, are you okay? You sound a bit defeated...

[Anonymous No.12804926]

Hoping to get some work checked, continuing off this assignment >>12804486


in 3b, i'm not sure what the deal is with (x(0), y(0) = (50,4). when I solved for the nonzero critical points of x and y, as seen here, >>12804594, I got x = 0.2/0.005 = 40 and y = 0.4/0.05 = 8. so im not really how to interpret what i'm given in this step, am I supposed to be adjusting anything?


and in four, when using the bluffton link below for the new equation, it looks exactly the same as the old one, basically. but i did find that the eigenvalues of the jacobian were complex


am i on the right track, or going about this all wrong?

helpful:
>https://homepages.bluffton.edu/~nesterd/apps/slopefields.html

[Anonymous No.12804931]

>>12804926
o wait i think i get it, i need to be looking at individual curves in the direction field and seeing what happens to the population

i could still use a second look at my work though

[Anonymous No.12805462]

I have a function of the following form:
[math]
c_1x_1 + c_2x_2 + c_3x_3 + c_4x_4
[/math]
that I want to maximize, but my domain of my x:s is limited. I know they come from some (small) set. However, there is an additional requirement. Picking some x for say, x_1, excludes some of the x:s in my domain to be assigned for the other variables. That is, I know the elements of my set of scalar x:s, but my domain of 4-vector x:s is unknown, until I pick an initial x, and it is then restricted.

E.g. say X = {1,2,..10}. Choosing x_1 = 1 may reduce my set to X = {2,3,4,5}. Picking x_2 = 2 may then reduce my set X = empty. Thus no vector x may start with (1,2,-,-).

Is there a good way to do this, or should I just bruteforce and try every combination to find my set of 4-vectors?