/sqt/ /qtddtot/ - stupid questions thread

[Anonymous No.12753409]

Previous thread: >>12739502

>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.12753493]

I have a room full of 100 couples, and the average iq is 100. Every couple is allowed to procreate, but nobody is pregnant yet. I get to decide the amount of kids each couple will have. My goal is to increase the average iq of the babies population only(not counting the parents).
All couples will have a minimum of 1 child and a maximum of 3.
In order to increase the average iq of the babies population to 115, how many couples on the left of the bell curve would I need to tell to only have 1 child, and how many on the right of the bell curve would I need to tell to have 3?

[Anonymous No.12753497]

>>12753493
To clarify, I'm only considering 1 generation.

[Anonymous No.12753498]

>>12753409
Is that from Kyuu-chan?

[Anonymous No.12753508]

Mathbros, what do/did you guys use to take notes in university? Do you do everything in notebooks/paper or do you use something like Notion or Dropbox Paper?
If you do use a tool, which one would you recommend? I'm not just worried about formulas/proofs/exercises/etc. but all forms of note-taking and organizing.
My hand gets tired easily from writing by hand so I'm looking for alternatives.

[Anonymous No.12753516]

>>12753493
Info is missing on the probability that a higher IQ couple produces a high IQ child. If no such info is available, automatic assumption is that any couple can produce any IQ in their children, therefore generational IQ mean never changes

[Anonymous No.12753546]

>>12753516
I'm not trying to be political, bro, so I don't know why you're trying to (((obfuscate))).
It's pretty obvious that genes express themselves with a degree of random variance. In real life it's obvious that a 100 iq couple might produce a child with 100 iq, or 95, or 105, all equally likely, but it's very unlikely that the child will have an iq of 130. Again, obviously, a 130 iq couple might produce a child with an iq of 135, just as likely as they would produce a child with an iq of 125, but they probably aren't going to produce a child with an iq of 160 or 105.

Pretty simple, right hymie? Now do the fuckin math for me

[Anonymous No.12753549]

>>12753508
Stop jerking off.

[Anonymous No.12753565]

>>12753546
Fuck off back to pol

[Anonymous No.12753610]

>>12753546
back to pol nigger

[Anonymous No.12753658]

>>12753546
>In real life it's obvious that a 100 iq couple might produce a child with 100 iq, or 95, or 105, all equally likely, but it's very unlikely that the child will have an iq of 130.
That's not how it works, my /pol/tard friend. The parents (and any ancestors) could've had a 160iq dormant gene for generations, or a more common 120-130.
>any couple can produce any IQ in their children
That does seem to be true with our current knowledge, yes.
>To clarify, I'm only considering 1 generation.
Yeah no, you definitely have no idea how any of this works.

[Anonymous No.12753727]

>>12753493
Assuming that IQ is normally distributed with mean 100 and standard deviation 15, and that a child's IQ is normally distributed with the mean the average of his parents IQ and standard deviation sill 15, you get the simplest reasonable model of your problem and it's STILL basically mathematically untractable.

[Anonymous No.12753733]

>>12753493
6 million

[Anonymous No.12753737]

What does /sci/ think of this? Is it accurate?
https://youtu.be/XjsgoXvnStY

[Anonymous No.12753936]

does anyone have the yukari version of this pic?

[Anonymous No.12753982]

>>12753936
This one?

[Anonymous No.12754028]

where do i find equilibrium constants for reactions? would rather have multiple options but at 25c 1atm is fine

[Anonymous No.12754034]

[math]
f(x) = (ax^3 + bx^2)*1/x^3
[/math]

If I try to derivate with this what happens to the a and b?

[Anonymous No.12754045]

>>12754034
Take a guess

[Anonymous No.12754048]

>>12754045
My guess is they fall away but is it literally the same as just x^3 + b^2 then?

[Anonymous No.12754053]

>>12754048
Have you tried using ax^3/x^3 = a and bx^2/x^3 = b/x?

[Anonymous No.12754075]

>>12754048
+ x^2 I mean
>>12754053
I don't follow. Why are we dividing by x^3?
If it was x^3 + x^2 with the product rule it would become 3x^2 + 2x, wondering how the a & b influence this

[Anonymous No.12754095]

I am totally retarded about STEM stuff. Some anon on /lit/ recommended me this lecture. But Jeremy England went from basic to complex physics real quick. The theory sounds so interesting from what I can understand so please recommend me some books I have to read in order to understand this lecture.

https://youtu.be/10cVVHKCRWw

[Anonymous No.12754103]

>>12754075
Because there's a *1/x^3 in your formula. So you wont need product rule, if your products cancel.
And the derivative of ax^3 is 3ax^2.

[Anonymous No.12754199]

>>12754103
Gotcha, I wanna do it both ways and see if I can do it correctly though. I just got 2a+b/x as a result from the product rule which seems wrong. Initial function has 1/x^2 at the end btw, wrote it wrong.

So without product rule:
ax^3/x^2 = ax? bx^2/x^2 = b? ax+b ? Wolfram alpha seems to say it's just a, not sure why.

With:
[math]
= (3ax^2 + 2bx)*1/x^2 + (ax^3+bx^2)*(-1/x^3)
= 3ax^2/x^2 + 2bx/x^2 + (-ax^3/x^3) + (-bx^2/x^3)
= 3a + 2b/x - a - b/x
= 2a + b/x
[/math]
Where'd I go wrong?

[Anonymous No.12754215]

Shrooms told me to become a physicist. How do I get out of wageslavery and study physics? I try to study after work but I'm exhausted and don't have much time. I have a bachelor's in electrical engineering and I'm currently at my first job out of college.

[Anonymous No.12754231]

>>12754199
For the first part: You have d/dx (ax+b) = a
For the second part: You forgot the *2 in the derivative of 1/x^3, so 3a+2b/x-2a-2b/x = a

[Anonymous No.12754242]

>>12754034
>>12754199
>>12754231
I'm very confused. Why isn't the answer just [math]-b/x^2[/math]?

[Anonymous No.12754256]

>>12754231
>d/dx
Wait what does this mean? How does the ax+b become a exactly?
> You forgot the *2 in the derivative of 1/x^3
I don't see where? The derivative of 1/x^2 is (-1/x^3) and as far as I can tell it's everywhere?

[Anonymous No.12754280]

>>12754242
anon said he miswrote the question, [math] f(x) = \frac{ax^3 + bx^2}{x^2} [/math].

>>12754256
[math] \frac{d}{dx}(\text{expression}) [/math] is standard notation for "the derivative of expression." Secondly, [math] \frac{d}{dx} \frac{1}{x^2} = \frac{d}{dx} x^{-2} = -2x^{-3} [/math] by power rule.

[Anonymous No.12754294]

>>12753409
What type of animal is that? If it doesn't exist, how much would it cost to make it real?

[Anonymous No.12754369]

>>12754280
I (kinda) understand the part without product rule now. Don't get the d/dx stuff but if you simply derivate ax+b the b and x fall away, I think, so a is left.
But the other part still makes no sense to me. Maybe I'll try again tomorrow.

[Anonymous No.12754397]

>>12754369
What is a*x+b graphically? a line
What is b? The intersection of the y-axis and the line
What is a? How steep the line rises
What is the derivative of f? The slope of f
What is the slope of a line? A constant
That's why d/dx(ax+b)=a

[Anonymous No.12754437]

>>12754369
d/dx is just notation. The following are all equivalent (if you've seen any of these notations):
The derivative of [math] f(x) = \frac{df}{dx} = \frac{d}{dx}f = f'(x) [/math]. It's just a simple way to write "take the derivative of the following expression."

The other bit follows from power rule. I assumed you had covered it, but in case not, the power rule states that if [math] f(x) = x^n [/math], where n is some real number, then the derivative of [math] f(x) [/math] is [math] n*x^{n-1} [/math]. Therefore, to find the derivative of [math] f(x) = x^{-2} [/math], we simply plug in [math] n = -2 [/math] into the power rule, which tells us that the derivative of [math] f(x) [/math] is [math] -2 * x^{-3} = \frac{-2}{x^3} [/math]. Does that help?

[Anonymous No.12754441]

>>12753508
a freaking apple ipad with notability. It just werks

also whats the worst average any of you /sci/fags have seen on an exam? My e&m midterm was 29% average with 22% passing. I pulled a fat 60 after cramming all night

[Anonymous No.12754449]

>>12754441
I meant 12% passing

[Anonymous No.12754455]

>>12754441
First quarter real analysis consistently had averages hovering around 50%. One time there was a nice bimodal distribution, with scores clustering around ~30% and ~60%.

[Anonymous No.12754470]

>>12754455
my gf took that and she said it was her toughest class in her masters. She said the professor would get lost and couldn't finish the problems frequently. As an engineering undergrad I doubt I'll ever take it but it sounds like fun

[Anonymous No.12754488]

What's a good drawing pad to write formulas and shit during meetings?

[Anonymous No.12754509]

>>12754488
No idea, /g/ is more likely to know.
If it's just about formulas you can use real-time Latex shit.
See https://www.youtube.com/watch?v=bk0J7WGwk90 for example.

[Anonymous No.12754519]

>>12754470
Having a shit prof makes it infinitely worse I'd imagine, thankfully both my profs for it have been great. The first one just liked to write hard tests I think.

I'd highly recommend it, I'm an EE and I find it really fun - it teaches you a different way to think about problems than you learn in engineering. If you can get it to count as a general technical elective or w/e, I'd definitely go for it, though not if you have multiple other difficult classes at the same time. Shit takes time, and was by far the toughest class I took in my undergrad (excepting one of the grad classes I took).

[Anonymous No.12754526]

>>12754509
I use xournal++ for texing on worksheets. It works well, but drawing a picture or a graph is fucking impossible with a mouse

[Anonymous No.12754722]

>>12753982
no it was one where yukari had the face of what I postee

[Anonymous No.12755082]

Would the expression for [math] X_{n+1} [/math] here be something like:

[math]
X_{n+1} = \begin{cases}

A_n & X_n = 0 \\

A_n + 1 & X_n > 0

\end{cases}
[/math]

[Anonymous No.12755095]

>>12755082
actually maybe something like:
[math]
X_{n+1} = \begin{cases}

A_n - 1 & X_n = 0 \\

A_n & X_n > 0

\end{cases}
[/math]

[Anonymous No.12755100]

>>12754519
>I'm an EE
Not that anon but what are some must take EE classes?

[Anonymous No.12755104]

>>12755095
although this does not make sense for [math] A_n = 0[/math]...

[Anonymous No.12755176]

>>12755100
It really depends on what you want to learn, since EE is so broad. I always recommend taking an intro level signal processing class, since you go through Fourier series & transforms (possibly Laplace & Z too depending on the curriculum), which are used all over the place in nearly every field. Signals classes tend to teach Fourier in the easiest way I think, since proving convergence isn't the focus, but rather developing an intuition for what you're actually doing - treating exponentials as an eigenbasis that you're projecting your signal on, and working in that eigenbasis because certain things are simpler. Because your looking at signals, there's also some functional analysis in there, as well as the basics of linear system theory since the motivation for all of this is LTI systems.

The class can be relatively math-y compared to other engineering stuff (I like math so it didn't bother me at all), but it's all highly useful. If you fall in love like I did, you can keep on going by looking into classes about filter design, communications, controls, and system theory.

[Anonymous No.12755286]

>>12755082
No, I think it would be more like this:
[eqn] X_{n+1} = \text{max}(X_n + A_n - (n \text{ mod } 2 + 1),\ 0) [/eqn]

[Anonymous No.12755310]

>>12755286
If it can be represented by [math]X_{n+1} = f(X_n, A_n)[/math] then by a theorem it is a discrete time markov chain;however, I have prior knowledge that this [math] X_n [/math] is NOT a DTMC, so it needs to be purely in terms of [math] A_n [/math]

[Anonymous No.12755368]

>>12754722
Never seen it, good luck finding it.

[Anonymous No.12755431]

Say I have the expectation values <a> and <b> is <ab> =<a><b>?

[Anonymous No.12755524]

>>12755431
Yes, if they're independent

[Anonymous No.12755561]

>>12755310
That's not possible.
I think you're confused.

[Anonymous No.12755615]

>>12755561
What you have specified is a DTMC, no?

[Anonymous No.12755661]

>>12755615
no, I don't think so
If you post the actual questions of problem 2, I could probably answer them.
And could you also post problem 1, because problem 2 seems to be referring to it.

[Anonymous No.12755703]

Guys, anyone, need help asap. Is this e-mail asking a prof if i can do my research project (thesis basically) formal enough and not rude or pedant?

Good Morning Professor Anon,
I am a first-year biology master's student here at 4Chan University, I am writing you to ask if it would be possible for me to join your research about synthesising anime catgirls for my research project.
I am not sure about what I should add to this e-mail, I asked my tutor but she has not answered yet. I am willing to meet (physically or digitally) to discuss details.
I will keep this e-mail short for now, and just let you know that I am very much interested in your research.
Being hopeful that I will hear back from you, I thank you for your time.
Best regards,

Anon.

Is this good enough? please help a bro out

[Anonymous No.12755718]

>>12755703
>I am not sure about what I should add to this e-mail, I asked my tutor but she has not answered yet.
I seriously hope you weren't going to actually put this in your email.

[Anonymous No.12755726]

>>12755703
>I am not sure about what I should add to this e-mail, I asked my tutor but she has not answered yet. I am willing to meet (physically or digitally) to discuss details.
Of course you would
>I will keep this e-mail short for now, and just let you know that I am very much interested in your research.
Of course you are

Just ask him if there's room for a master's student in his group.

[Anonymous No.12755737]

>>12755718
Why not? maybe he expects me to tell him why i'm interested and so on, but maybe he doesn't (at least not via e-mail), so I'll just cut the crap (the country I'm studying in is notorious for its citizenz' directness apparently so I don't think a mail like this would be seen as weird).
>>12755726
I mean yes it's obvious, but it's short enough already, is it? I don't want to sound rude by just asking if there's a place for me, it's not like a job.
what would you write?

[Anonymous No.12755738]

>>12755661
The only thing relevant from problem 1 is the distribution of An, which is P(An = 0) = 3/5, P(An = 1) = 1/5, P(An = 2) = 1/5

here is the rest of problem 2.

[Anonymous No.12755740]

>>12755703
Delete everything after the first sentence up to but not including "Best regards," and replace with "Is there a time in the next week or so that we could meet to discuss details?"

[Anonymous No.12755763]

>>12755740
even the hopeful part?

[Anonymous No.12755764]

>>12755737
>what would you write?
Don't write a fucking essay, nobody likes writing or reading emails.
Tell them you're interested and if there's room for you you'd like to have a talk.

[Anonymous No.12755776]

>>12755763
Yes.

[Anonymous No.12755789]

>>12755764
>>12755776
alright, deal.
BUT I'M LEAVING THE I THANK YOU FOR YOUR TIME.
also what the fuck do I tell hima t the meeting, I'm a fraud, idk anything, i'll read some papers beforehands I guess

[Anonymous No.12755798]

>>12755789
Just know what they're doing and how the basics work.

[Anonymous No.12755801]

>>12755789
Tell him what about his work interested you [synthesizing beings, working with catgirls, etc.] so that he can get an idea for what you are looking to do, and ask him to talk about that. If you don't have any specifics now, then start reading or skimming his publications to see what you'd like to work on. Profs love talking about their work, so just get him talking about his own stuff and engage with him in conversation, and you'll be fine.

[Anonymous No.12755831]

>>12755798
>>12755801
thank you very much, you guys have been really helpful.
I thank you for your time.
Best regards,

Anon.

[Anonymous No.12756080]

>>12755738
(a) 1/5
(b) 3/5
(c) It's not a DTMC, because the probability of [math] X_{n+1} [/math] being a certain value does not solely depend on [math] X_n [/math], it also depends on the state of the links.
(d) I dunno

[Anonymous No.12756150]

>>12756080
thanks I got D, but could you elaborate more on how you got the values for a and b?

[Anonymous No.12756513]

What's the worse case of crappy scientific headline and article that has almost nothing to do with the actual study it cites you guys have seen recently?

[Anonymous No.12756519]

>>12753565
>>12753610
>>12753658
samefag

cry more you mutilated inbred freak

[Anonymous No.12756531]

EE student looking for some elective recommendations/advice/opinion on which courses to take.
I can pick 6 lecture electives from the list.
What I'm currently thinking of is:
1) Electric Power Engineering
2) Element of Power System
3) Probably Digital Signal Processing from this kind anon's advice >>12755176

The rest is free game!
I can also choose 2 from this smaller list and not have it impact the 6 choices I have:
A) Antennas and Fiber Optics
B) Electronics II
C) Control and Feedback Systems
D) Solid State Devices

[Anonymous No.12756546]

>>12756531
Advanced Optics sounds fun.

[Anonymous No.12756549]

>>12753727
So you understood the question, now answer it you fuckingcracker liberal.

[Anonymous No.12756587]

Why is 4chan so faggoty about post deletion?

[Anonymous No.12756710]

>>12755176
>I always recommend taking an intro level signal processing class, since you go through Fourier series & transforms (possibly Laplace & Z too depending on the curriculum), which are used all over the place in nearly every field.
What the hecc, the two are used all over the field? I have to study this ahead of time then!
>Signals classes tend to teach Fourier in the easiest way I think, since proving convergence isn't the focus, but rather developing an intuition for what you're actually doing
Okay now I must take this class desu, developing an intuition is my top priority, hopefully, the professors are not doodoo.
>The class can be relatively math-y compared to other engineering stuff
I'm currently reading Sedra's microelectronics book and I swear that book is more math than engineering heh... I think I'll be fine with extra math stuff (unless they add in vector calculus... God I need to get better at that).
>it's all highly useful.
Could you give me some examples? I'm genuinely curious, it's okay if you don't though!
>If you fall in love like I did, you can keep on going by looking into classes about filter design, communications, controls, and system theory.
Noted! I have not yet taken any of those classes but controls and systems theory is like a secret guilty interest for me.
Do you visit ohm? Just curious, though it's pretty much 99% electronics.

[Anonymous No.12756814]

>>12756710
The class is mathy, since you usually do prove the properties / dualities of Fourier transforms (FTs), but it's not vector calc, mostly just manipulating integrals. They almost always teach convolution too, which is an operation that has an unwieldy integral definition if you're not used to it.

As for uses, they're all over the place, from physics to engineering. In physics, one possible application my old prof liked to bring up was how the Heisenberg uncertainty principle could be mathematically modelled as being a FT pair - the PDF of the momentum & position of a particle are related in that one is the FT of the other. If you ever study differential equations, FTs will come up since they can provide a super easy way to solve ODEs if the structure is right, and give us ways to solve certain classes of PDEs that you wouldn't be able to otherwise. If you study linear systems, which can be used to model to a wide variety of mechanical, electrical, or chemical systems, the Laplace & Z transforms (same basic idea as the FT) will also come up as highly helpful tools for designing and analyzing those systems. We live in a world of frequencies, and understanding those frequencies through Fourier is immeasurably helpful.

Since I love talking about this, I'll give you one quick example, the ODE thing from before. Suppose that you have some gross nth order ODE. Differentiation in time is equivalent to multiplication by the frequency variable [math] \omega [/math], so by converting your equation into FTs, the ODE becomes a simple algebraic equation. All you need to do is solve for the FT of your function (trivial), and then convert your answer back from FTs into function of time. Frequency domain math is all about solving the easier problem, which is part of why my lazy ass fell in love with it.

Also no, I don't go to ohm, my circuits fundamentals are fucked because of a really shitty prof (and I've never had to really use it in other classes yet).

[Anonymous No.12756836]

>>12756814
>mostly just manipulating integrals. They almost always teach convolution too, which is an operation that has an unwieldy integral definition if you're not used to it.
More stuff to study then!
>Differentiation in time is equivalent to multiplication by the frequency variable ωω \omega , so by converting your equation into FTs, the ODE becomes a simple algebraic equation. All you need to do is solve for the FT of your function (trivial), and then convert your answer back from FTs into function of time.
What the hecc, since I'm currently just starting differential equations, this sounds like cheating and is super useful. Sorry I didn't understand the stuff you said before tho, but soon I will...
>my circuits fundamentals are fucked because of a really shitty prof
Heh, same, now I'm dying in a class that uses it.

Is there any signal processing textbook/resource you'd recommend? I'm always getting interested in new things because EE is so freaking massive.

[Anonymous No.12756908]

>>12756836
Yes, it's so easy it does feel like cheating sometimes. Doesn't work well for non-homogeneous equations though, because you might end up with an expression in frequency that doesn't have an easily found inverse transform.

>Heh, same, now I'm dying in a class that uses it.
Yeah, that'll probably happen once I start taking the required electronics design courses. Op amps I don't really get, and although I understand filters pretty intuitively, I don't get how inductors or capacitors have filtering qualities outside of the "mass" argument (but that doesn't tell me how to design a lowpass filter using circuit elements).

>Is there any signal processing textbook/resource you'd recommend?
For beginners, Oppenheim "Signals & Systems" is a good introductory text. It goes through convolution, defining LTI systems, Fourier series, Fourier transforms (continuous and discrete time), Laplace & Z transforms, and a little taste of feedback systems at the end to get you interested in controls. If you want something a little more hardcore, you could go Oppenheim "Discrete Signal Processing," but that one (understandably) doesn't really do continuous time stuff. Dunno about online resources.

[Anonymous No.12756933]

I am a physicist and I have recently grown interested in hydrogen fuel cells, namely, how do they work how are they built etc,etc.

Are there any books that you would care to recommend about them?

[Anonymous No.12757060]

>>12753409
How does IQ, as the culturally accepted 'standard' of intelligence, not scale linearly despite both using a linear measurement system and measuring an attribute that ranks upwards?

[Anonymous No.12757109]

>>12756908
>Yes, it's so easy it does feel like cheating sometimes.
It's like when my teacher in HS forced us to do derivatives the long way with limits and +h thing and then we learned the normal way of doing it—feels great but also kind of want to revisit those days.
>Yeah, that'll probably happen once I start taking the required electronics design courses
You should definitely go on ohm when you take those courses then, they helped me a lot in electronics including theories and concepts. Espescially your op amps, capacitor and inductor filter question, you should definitely ask there if you're ever feeling it.
>For beginners, Oppenheim "Signals & Systems" is a good introductory text. It goes through convolution, defining LTI systems, Fourier series, Fourier transforms (continuous and discrete time), Laplace & Z transforms, and a little taste of feedback systems at the end to get you interested in controls.
Thank you senpai, really appreciate it!

[Anonymous No.12757193]

Which is better, science and math classes at the local university, or self study?

[Anonymous No.12757530]

>>12753493
Can someone answer this question? I'm curious too.

[Anonymous No.12757560]

>>12757193
if by local university you mean community college, then do that because the classes are dirt cheap and it'll get you off the chan boards for an hour or two. unless you're a fucking phoneposter.

[Anonymous No.12757998]

What does it mean if I'm good at numbers (can understand things very well when expressed solely in numbers) and awful in scientific abstracts? Are there any studies where I could fit in easily?

[Anonymous No.12758466]

>>12757530
I can't, the guy asking is a prick.

[Anonymous No.12758502]

>>12757193
why not both?

[Anonymous No.12758524]

>>12757998
It means you're good at arithmetic. You would be good at careers like accounting.

[Anonymous No.12759194]

the last two lines are a typo, right? [math]a-s<0 \right a<s = s>a[/math].

from Paul's online math notes, Laplace Transform section within the diff eq stuff.

[Anonymous No.12759247]

>>12759194
No, they're correct. Note that both state exactly the same thing; the first follows directly from evaluating the antiderivative of e^(a-s)t at infinity and zero and noting that a-s must be negative for the integral to converge, the second is just rearranging it.

[Anonymous No.12759436]

>>12759247
ah ok, thanks. i understood the were stating the same thing, but not the rest.

last question, how do i find the first term in this? I can see that the last term is the combined fraction of [math]-2sin(5t)-2cos(5t)[/math], but I'm absolutely lost as to how to find the first term, it doesn't resemble anything in the table of transforms I've seen.

[Anonymous No.12759671]

In Dirac Notation how do I deal with [eqn]\sum |a> |b> <c| <d|[/eqn] I understand that [math]|b> <c|[/math] forms a matrix but I dont know what the combination does.

[Anonymous No.12759678]

>>12759671
That expression is illegal unless there's an implicit tensor/direct product between a and b, c and d.

[Anonymous No.12759725]

This is probably too much to ask because you'd probably have to work it out yourself but I am stuck. I have some equations of equilibrium and what P is in terms of [math] \alpha [/math] and [math] \theta [/math].
[math] \sigma F_x = -F_k - Wsin\alpha + Pcos\phi = 0[/math]
[math] \sigma F_y = Wcos\alpha - N + Psin\phi = 0[/math]
and
[math] P = \dfrac{Wsin\alpha - \mu_k Wcos\alpha}{cos\phi - \mu_k sin\phi}

Hope this latex shit works.

[Anonymous No.12759732]

>>12759725
Oh and heres the problem

and attempting P again [math] P = \dfrac{Wsin\alpha - \mu_k Wcos\alpha}{cos\phi - \mu_k sin\phi} [\math]

[Anonymous No.12759736]

>>12759732
[math] P = \dfrac{Wsin\alpha - \mu_k Wcos\alpha}{cos\phi - \mu_k sin\phi}[/math]

[Anonymous No.12759778]

>>12759725
There's a preview button to make sure your tex works out in the top left corner of the reply window.

For part (a), you need to find the phi that minimizes your P. Since phi is only present in the denominator, all you need to do is maximize the denominator, [math] \cos(\phi) - \mu_k \sin(\phi) [/math] which can be done by setting its derivative wrt phi to 0 (and verifying that your found value of phi is a maximum, not a minimum).

Part (b) is trivial once you do part a.

[Anonymous No.12759803]

This is the full expression, I reasoned that theres an implied direct product as the second term is required to have the same dimension as the first for the Hamiltonian to make sense. So I think whats happening is two matrixes multiplied by direct product.

[Anonymous No.12759816]

>>12759778
tyvm. while i am in statics and i still dont really understand maximizing and all that, i could follow the process and got the right answer. hopefully thats ok for an engineer

[Anonymous No.12759892]

>>12759816
You should probably understand the maximization in this problem, since it's pretty simple. I think it's pretty clear how maximizing our denominator results in a minimum for P. Since our denominator [math] \cos(\phi) -\mu_k \sin(\phi) [/math] is a continuous & differentiable function of phi, by interior extremum theorem we know that it must attain its maxima and minima when its derivative is equal to 0, so we just find the phi for which that condition is met and check where it attains a maximum or minimum there.

If you haven't seen this theorem before and want a quick intuition for it, suppose that some continuous & differentiable [math] f(x) [/math] achieves its maximum at some [math] x_0, [/math] and [math] f'(x_0) > 0 [/math]. Then if you take a step of length delta to the right that's small enough, [math] f(x_0+\delta) \approx f(x_0) + \delta f'(x_0) > f(x_0), [/math] so [math] x_0 [/math] can't be a maximum. The same style of argument hold when [math] f'(x_0) < 0 [/math] by taking a step to the left instead of the right, and so if [math] x_0 [/math] is a maximum, [math] f'(x_0) = 0. [/math]

[Anonymous No.12759942]

>>12759892
Yea all this calculus stuff keeps coming up. I better have a firmer grasp of the basics. Thanks for your help and encouragement anon.

[Anonymous No.12759985]

>>12759803
[math]V_{ab;cd}[/math] looks to be a tensor which will reduce to a matrix once used to cancel the [math]|c>_j\ {}_{j}<|d|[/math]. Then you do the same again for [math]V_{ab}[/math].

[Anonymous No.12760018]

>>12759803
>So I think whats happening is two matrixes multiplied by direct product.
...no, not quite.
Basically, [math]|a \rangle | c \rangle[/math] is just a ket, and [math]\langle d | \langle b|[/math] is just a bra, but they're a ket and a bra in the tensor product (it's most likely a tensor product rather than a direct product), so it's just *one* matrix (on the tensor product).
>>12759985
No.

[Anonymous No.12760029]

>>12760018
>inb4 why a tensor product instead of a direct product
Direct products aren't actually relevant for QM.

[Anonymous No.12760114]

>>12759436
> last question, how do i find the first term in this?
In what?

[Anonymous No.12760135]

why does the HR diagram go the opposite way on the x axis??

[Anonymous No.12760143]

>>12759436
>>12760114
sorry forgot image.

[Anonymous No.12760151]

>>12760135
It's the 'right way' if you consider wavelength instead of temperature

[Anonymous No.12760181]

In 2 dimensional cartesian coordinates taking any relation and switching all x with y and all y with x simply just reflects the relation across the line y=x, correct?

[Anonymous No.12760605]

>If a singly ionized Xenon gas is used for an ion drive engine, which has the ions pass thru an accelerating voltage of 10 KV. How many atoms per second do I need to send out to get a thrust of 91 mN? ( Hint use F*dt= m*dv - comes from F=ma and a=dv/dt).
# of atoms needed per second
Not even sure how to start this

[Anonymous No.12760607]

>>12760181
Yes

[Anonymous No.12760624]

>>12760143
[eqn]
\mathcal{L}^{-1} \left\{ s^{-{5 \over 2}} \right\} = {4 \over 3 \sqrt \pi} t^{3 \over 2}
[/eqn]
More generally,
[eqn]
\mathcal{L}\left\{ t^q \right\} = \frac {\Gamma (q+1)} {s^{q+1}}
\\ \implies \mathcal{L}^{-1}\left\{ \frac {\Gamma (q+1)} {s^{q+1}} \right\} = t^q
\\ \implies \mathcal{L}^{-1}\left\{ \frac 1 {s^{q+1}} \right\} = \frac {t^q} {\Gamma (q+1)}
\\ \implies \mathcal{L}^{-1}\left\{ \frac 1 {s^k} \right\} = \frac {t^{k-1}} {\Gamma (k)}
[/eqn]
If k is a positive integer, Γ(k)=(k-1)!.

[Anonymous No.12760665]

[math]V_r=2r^2-3r+7[/math] is a Potential function. Find E(r) at r=2 meters . E=______V/m.
If [math]E_r=5r^3-10r^2+6r-8[/math] is the Efield strength, find the work done in moving a + 3 uC charge from r = 1 meter to r = 2 meters. U=____joules

I just need to know how to manipulate these, for the second one I integrate from 1 to 2 right? Idk about the first.

[Anonymous No.12760675]

>>12760605
Energy = qV (q = charge, v = voltage).
Energy = (1/2)*m*v^2 (m = mass, v = speed).
qV=(1/2)*m*v^2 => v=√(2qV/m)

F*t = n*m*v = n√(2qVm) (F = force, t = time, n = number of atoms)
=> n/t = F/√(2qVm)

F=91e-3 N, q=1.6e-19 C, V=1e4 V, m = 2.18e-25 kg.
=> n/t=3.45e18 s^-1.

[Anonymous No.12760701]

>>12760665
(1): [math]E = -\vec{\operatorname{grad}}V[/math]
(2): [math]W = \int_{1}^{2} qE(r)dr[/math]

[Anonymous No.12760714]

>>12760624
thanks anon :-)

[Anonymous No.12760900]

I have 10 lbs of oxalic acid that "expires" this March. What sort of synthesis/other experiments could I do with it? Was thinking of just making some esters or something but that's boring and I've done it before. I would try oxaliplatin but that's a bit complex.
>inb4 eat it

[Anonymous No.12761997]

Is.. Is a kilowatthour a constant..

[Anonymous No.12762298]

>>12754028
Your textbook should have some. In case it doesnt a quick search for equilibrium constants on goigle scholar shoul give you what you want quick

[Anonymous No.12762392]

What do you guys think of the Data Science field?
To those in it, what does the average work day look like?

[Anonymous No.12762546]

If pic related is a toddler's skull, then would a toddler's head theoretically explode into a firework of teeth if I hit it really hard on the jaw with a baseball bat or something?

[Anonymous No.12762626]

I understand the first part of the proof in pic related (that alpha^2 can't be less than 2).
But, I absolutely have no idea how the parts where I put the arrows work.
[math]\frac{2\alpha}{n_0} < \alpha^2 - 2[/math], which makes sense (pretty much copy-paste from the first proof).
What I don't understand is the next line. He has only shown that [math]\frac{2\alpha}{n_0} < \alpha^2 - 2[/math], not that it is equal, so shouldn't the next line be:
[math](\alpha - 1/n_0)^2 > \alpha^2 - 2\alpha/n_0 < \alpha^2 - (\alpha^2 - 2) = 2[/math], which would make the entire thing pointless?

[Anonymous No.12762642]

>>12761997
It's a quantity of energy.
By definition, yes.

[Anonymous No.12762670]

>>12762626
you missed a minus, your < would be a >
But yes, the = should be wrong

[Anonymous No.12762700]

>>12762670
>you missed a minus, your < would be a >
Thanks for the reply. I'm having a total brainlet moment right now and I can't figure it out.
If I add a minus, then [math]-\frac{2\alpha}{n_0} < \alpha^2 - 2[/math], and the equation below that would make sense now, but how can I multiply just one side of the equation by -1 and turn the inequality sign around? Or in other words, how do I know that [math]-\frac{2\alpha}{n_0} > \alpha^2 - 2[/math] just because [math]\frac{2\alpha}{n_0} < \alpha^2 - 2[/math]

[Anonymous No.12762781]

what are your favorite non-reddit STEM fields?

[Anonymous No.12762800]

>>12762546
No the force would propel the teeth further into the skull, you'd have to somehow cause an explosion outward. Your teeth explosion in this case would be masked by your murder charge and other face gore flying around.

[Anonymous No.12762824]

>>12762800
What about a good swing across the face? Would it explode into a barrage of teeth then? Child bones are just cartilage, right?

[Anonymous No.12762831]

>>12753409
Six hours. Unable to solve a single task. I fucking hate myself.

[Anonymous No.12762838]

>>12762831
Im in the same boat now, I figure its because i blew off solving problems for cheating them out with solution manuals and the internet. I never built the intuition to solve problems.

[Anonymous No.12762841]

>>12762838
Hehe I failed for hours even with Internet. The curse of sub 100 iq

[Anonymous No.12762849]

>>12762700
He's saying that the equation in the picture is indeed wrong, but to fix it you need to replace the = sign with a > sign (whereas you replaced the = sign with a < sign).
If you're asking why it is the case that 2a/n < a^2 - 2 implies a^2 - 2a/n > a^2 - (a^2 - 2), it's simple algebra:
2a/n < a^2 - 2
>multiply both sides by -1 and flip sign:
-2a/n > -(a^2 - 2)
>add a^2 to both sides:
a^2 - 2a/n > a^2 - (a^2 - 2)

[Anonymous No.12762853]

>>12753409
Hey it's grug again. Why is the solution of x''(t)-6(x(t))^2=0, x(0)=0 x'(0)=0 an elliptic function? I saw in a book that a solution is x=0, x=t^-2, and x=-t^-2.

[Anonymous No.12762889]

>>12762853
The general solution is some elliptic function however with those boundary conditions it simplifies to [math]x(t)=\pm\dfrac{1}{t^2}[/math].

[Anonymous No.12762914]

>>12753409
Squish Cat! :O

[Anonymous No.12762975]

>>12762849
>If you're asking why it is the case that 2a/n < a^2 - 2 implies a^2 - 2a/n > a^2 - (a^2 - 2), it's simple algebra:
>2a/n < a^2 - 2
>>multiply both sides by -1 and flip sign:
>-2a/n > -(a^2 - 2)
>>add a^2 to both sides:
>a^2 - 2a/n > a^2 - (a^2 - 2)
oof yeah I could't make sense of this part b/c I inserted the equation wrong, thanks for taking the time to write it out for me, I was having a total stroke, it makes sense now.

[Anonymous No.12763001]

>>12762889
Thank you.

[Anonymous No.12763036]

>>12762889
Really?
The solution is not differentiable at 0. Shouldn't the solution of a differential equation be differentiable?

[Anonymous No.12763039]

>>12763036
Scratch that I'm an idiot

[Anonymous No.12763172]

Is there anything i can dilute/thin dielectric grease with while keeping it insulating?

[Anonymous No.12763244]

Hi.
I'm not a scientist or engineer.
I've noticed modern plane engines seem to have teeth on the back side.
I did some googling and it seems it has been implemented to make engines less noisy. There doesn't seem to be a technical explanation online. The only answer as to how it works is "it changes the nature of the produced turbulence".
My questions are:
>1) Is there a resource I can consult to better understand how it works? It would be neat if somebody without a degree could understand it, but I guess that will probably not be the case. Does it maybe work by creating a group of small vortices that somewhat cancel each other rather than one big vortex?
>2) Could this technology be applied to the end of other tubes where gases of different speeds meet? Examples: exhaust pipes of internal combustion engines, muzzles of guns. Why or why not?

[Anonymous No.12763502]

>>12763244
> There doesn't seem to be a technical explanation online.
Because if I had to guess that is because it is a design covered by some kind of patent so precisely how it works would be a manufacturers secret. Turbulence in general is a very difficult topic which is why Navier Stokes is a Millennium Prize problem.

[Anonymous No.12763512]

Is psychology our /sci/ filter for brainlets?

Nobody knows about science, nor philosophy of science. People can show correlations all day, and false metaphors too. But too prove a causal link in the form of theory is quite challenging.

e.g. 'don't drink the public kool-aid'
or 'invisible symptoms'

[Anonymous No.12763560]

>>12763244
Why don't Boeing planes don't stay in the air

[Anonymous No.12763573]

If we were to send a signal to find aliens a standard mathematical such as pi or e would be ideal, right? But then what base would be best to use? We use 10 but would binary be better? How about base 8? That's a power of 2. It's pretty useful in calculation.

So what number would you send for the best results, and what base would you use?

[Anonymous No.12763734]

>>12763573
> "If we were to send a signal to find aliens ..."

[Anonymous No.12763847]

>>12760701
Sorry, what does gradV mean
Also is the integral multiplied by k?

[Anonymous No.12763853]

How do I resolve a vector into it's xyz components just knowing its xyz magnitudes, my brain isn't working rn

[Anonymous No.12763864]

>>12763847
>what's grad V
[math]grad \ V = \nabla V[/math]

[Anonymous No.12763868]

>>12763853
Wait I just multiply by the ratio of the vector magnitude and the directional magnitudes, duh.

[Anonymous No.12763870]

>>12763847
In this case [math]E = - \frac{dV}{dr}[/math]

[Anonymous No.12764288]

*sigh*

ughhhh

did pepe raise to demotivation status yet?

[Anonymous No.12764299]

Now if a bitch sucks yo' dick, for five dollars per square inch
and gets forty dollars, includin a five dollar tip
How big was the dick she just sucked? (Say what?)
Say how big was the dick she just sucked? (What?)......

If you remove every living animal out of the sea
then wouldn't the world's ocean water level decrease?
This means the planet wasn't three-quarters water (that was deep)
This means the planet wasn't three-quarters water (that shit was deep)
It's nigganometry.

[Anonymous No.12764334]

>>12762889
With those boundary conditions it simplifies to x(t)=0.

If you set x(t)=k/t^2, then x''(t)=6k/t^4 and 6x(t)^2=6k^2/t^4, so the ODE is satisfied if k=k^2 => k∈{0,1}, i.e. x(t)=0 and x(t)=1/t^2 are solutions (but x(t)=-1/t^2 isn't). Note that x(0), x'(0) and x''(0) are undefined. x'(t)=-2k/t^3, so the boundary conditions must satisfy 2x(t)+t*x'(t)=0 in order for x(t)=1/t^2 to be a solution.

Finding a general solution leads you to the integral
[eqn]\int \frac 1 {\sqrt{4 x^3 + k}}\,dx = t[/eqn]
where k is a constant of integration from a previous integral. if k=0, the integral is straightforward and you get -1/√x=t+C => x=1/(t+C)^2. Note that this satisfies the ODE for all C (but still doesn't admit x(0)=0 or x'(0)=0). If k≠0 then you get an elliptic integral.

[Anonymous No.12764605]

torque has never made sense to me
I'm trying to design a windmill generator.
If I have a windmill standing upright but unsupported, and the wind imparts a force on the face of the fan blades, intuitively the fan is going to fall over backwards, in the direction the wind is blowing

so why then does the actual torque fuck off into a completely orthogonal, unrelated direction???

[Anonymous No.12764630]

>>12764605
oh wait it's gravity making it fall nevermind

[Anonymous No.12764649]

>>12764630
>>12764605
wait no not nevermind, once the thing starts falling the torque is just caused by gravity instead of wind
and it's *still* not facing the same direction that the windmill is falling
so what gives

[Anonymous No.12764712]

>>12764605
Torque as you've indicated is just a notational thing to easily indicate the axis of rotation & magnitude of the torque, you read it using the RH rule to figure out the direction of the rotation of the body. It's also useful when drawing 2D diagrams to clearly show the directions of rotation without mucking up the diagram too much.

[Anonymous No.12764822]

Dumb question time.
Do you guys allow yourselves to fail?
I feel like especially in my STEM classes (particularly engineering), I tried my best to 'not fail' so that I don't fall behind the curve but I feel like that mindset is fucking me over as I don't focus on succeeding either. Sorry if that doesn't make sense, I just feel inhibited by this 'just don't be so below the curve that you fail hard' mindset.

[Anonymous No.12764918]

Really stupid hydro-static force problem: A vertical end of a full swimming pool has the shape of given in the following figure. Find the force exerted by the water in this end of the pool.

Pls need help

[Anonymous No.12764930]

>>12763502
I see.
Tbh I just wanted to know if it would make sense cnc'ing a muzzle device like that for a rifle for my own use. I guess I can just try it out myself and see what happens.

[Anonymous No.12765041]

What does it mean to solve by introspection?

[Anonymous No.12765048]

What does it mean to solve by inspection?
Deleted my previous post because I couldn't read.

[Anonymous No.12765067]

>>12765048
It means "look at the problem and think instead of applying some method you were taught".
Pretty sure second collumn is -3/2 times the first, that should deliver the rest.

[Anonymous No.12765089]

>>12765067
I-I'm sorry anon... I don't know how I got the answer but it's 3/2 on top of 1 like this:
[3/2]
[1]
I tried to solve for it manually and I got x=-3/2 but I don't understand why it's positive aaaaaaaaaaaaaaaaaaa. I'm sorry I'm stupid...

[Anonymous No.12765093]

>>12764918
here's a tip, does width of the pool matter, and if so, how?

[Anonymous No.12765106]

>>12765089
Nah, no biggy.
Juggling the intuition "matrix multiplication is just inner products with the row vector and the provided vector" and the other intuition "the vector with a 1 in entry i and zeroes everywhere else is mapped to column i" is hard when you're starting out.

[Anonymous No.12765108]

>>12764822
Failure is a part of life, anon. Focus on succeeding at your goals (whatever those are), and you'll find yourself actually succeeding more often (as opposed to just not failing). Of course sometimes you'll fail, but as long as you learn from those mistakes then it's not like that test was wasted - you got something out of it, whatever lessons you learned.
>t. bottomfragged on a test before, still came out with an A in the class

>>12765089
Just think about it for a moment, or do the multiplication out by hand. It has to be positive because you need to cancel out the columns, not just match them to be equal (which is what -3/2 gives you).

[Anonymous No.12765125]

>>12765093
If you are talking about the one that exttends 'into' the computer, i don't think so. However, I guess the width of the incline does need to be taken into account as it changes. I could come up with:

[math]F = \rho g \int_0^4 (8-y)\cdot x \ dy [/math]

Where 'x' is the width. However, this width only applies for the 'bottom triangle', right? I tried adding this force to the top rectangle but it just does not really work.

[Anonymous No.12765137]

>>12764299

1.)
$5/square inch ->$40: $35+$5 tip
dick = 7 sq in.
assume:
-she wants the most money, so whole dick went in, and
-a dick ratio of length-to-width of 7-1
cyllindrical dick shape


surface of cylinder without ends = 2 pi r h= 2 pi (d/2) h = pi d h

hence h = 7 / pi d

multiply by h on both sides and substitute the assumed h/d ratio

h^2 = 7^2 / pi

hence, dick length, h = 7 / (pi)^(1/2)

or should we assume a conical shape?


2.) organisms on land and in sea are mostly water

[Anonymous No.12765154]

>>12765125
The given answer is like 125,400 lbf/ft3 though. I'm sorry, they love giving us the problems in imperial units

[Anonymous No.12765205]

Ok i want to know if I'm a fucking dumbass. Suppose [math] Ext^1(A,B) = 0, \forall modules B[/math]. I want to prove A is projective. Let [math] 0\to L \to M \to N \to 0[/math] be a short exact sequence. You get a long exact sequence in Ext, [math] 0\to Hom(A, L) \to Hom(A, M) \to Hom(A,N) \to Ext^1(A, L) \to Ext^1 (A, M) \to Ext^1(A, N) \to \cdots [/math]. Then, immediately by assumption, you get a SES [math] 0\to Hom(A, L) \to Hom(A, M) \to Hom(A,N) \to 0 [/math] so A is projective. Is it really this easy or is there something obvious I'm missing?

[Anonymous No.12765208]

>>12764918
[math]dF=p\cdot dA = \int_0^8 w\rho g dh = \int_0^4 w\rho g dh + \int_4^8 w(h)\rho g dh[/math]
Now parametrize [math]w(h)[/math] as [math]w(h)=3(8-h)[/math] for [math]h \in [4,8][/math]
[math]
\int_0^4 12 \rho g \,dh +\int_4^{8} 3(8-h)\rho g \,dh\\
=12 \rho g h |_0^4+24h \rho g |_4^8-3h^2 \rho g|_4^8 \\
=140000 ish[/math]
fucking burger units
Does this make any sense whatsoever?

[Anonymous No.12765220]

>>12765108
>Just think about it for a moment, or do the multiplication out by hand. It has to be positive because you need to cancel out the columns, not just match them to be equal (which is what -3/2 gives you).
W-wait, why do I need to cancel them out?
Forgive me if I'm wrong, -6(3/2) = 9 -> -9 = 9 -> 0 = 0 which would give one of those trivial solutions r-right? Because I can cancel out row 2 and row 3... (I also don't get why the 1 is there desu).
>>12765106
Juggling the intuition "matrix multiplication is just inner products with the row vector and the provided vector" and the other intuition "the vector with a 1 in entry i and zeroes everywhere else is mapped to column i" is hard when you're starting out.
Y-yeah I'm just trying to wrap my head around some of this stuff. It doesn't help th at the website homework system is based off a different textbook so half of the time I literally do not understand what they're saying...

[Anonymous No.12765223]

Is anyone into geometry? I can take a picture of some of my copy of On the Revolutions of Heavenly Spheres if someone wants to take a stab at resolving this.

I don't think it's a dumb question, but no one replied when I made a thread ;_;

[Anonymous No.12765225]

>>12765223
That's Copernicus by the way, not ancient just not very modern. Again, it's a problem as regards triangles, perhaps, or knowing certain angles.

A plus would be someone who is familiar with this sort of thing.

[Anonymous No.12765229]

>>12765205
Looks correct to me.

[Anonymous No.12765237]

Would it be possible to physically hack and take over an active satellite in LEO to broadcast AM/FM radio across the world?
Is this even remotely possible?

[Anonymous No.12765241]

Should I get a masters in statistical learning ?

[Anonymous No.12765244]

>>12765241
Do you want a masters in statistical learning?

[Anonymous No.12765248]

>>12765244
I guess so but I’m afraid of how specific and how fast it could all disappear or become old (?)

[Anonymous No.12765253]

>>12765248
If that happens to be the case (which I think is highly unlikely) your skills would transfer to related fields.

[Anonymous No.12765257]

>>12765253
Ok, thanks for the take man, you’re right

[Anonymous No.12765260]

>>12753409
What happens if you have vodka in your nose for a minute?

Do any med fags know?

[Anonymous No.12765272]

>>12765208
Yes yes yes THANK you anon! I think I am getting it now. How do you get the 140000ish tho? I guess the end bit must be

[math] \frac{3}{2}h^2 \rho g [/math]

But even with that it is not close. Are you using 62.4 as the (density x gravity)?

I agree, fucking burger units.

[Anonymous No.12765275]

fuck I really don’t want to learn Latex

[Anonymous No.12765280]

>>12765275
Do you need to learn it though?

If you do, Overleaf has a rich text option alongside the normal syntax. Maybe you can start with that and then get familiarized with it. It is not that hard. VSCode also has some snippets and extensions that make everything faster.

[Anonymous No.12765305]

>>12765272
>>12765208
fuccin nerdz

[Anonymous No.12765732]

Bit out of the left field for most questions asked here but I have to ask:
How do you balance learning and trying to get a good grade? I often find that I'd rather just study the problems that uses a theorem than to study the theorem itself because of time constraints. Going straight to the practice problems rather than taking the moment to explore what I've just learned, which honestly isn't too good.
Sqtbros, please give me your opinions. I've heard a bunch of people in my major (EE) say that they "don't care about the grade" and only care about actually learning the coursework and they seem genuinely happy. I'm on the other end where all I care about is the grade and it's honestly a bit cold on this side.

[Anonymous No.12765774]

>>12765220
You need to cancel them out because that's what Ax = 0 is asking you to do. If you write out all the matrix multiplications and set up your resulting equations, if x = [x1 x2] you get that

[math] -6x_1 + 9x_2 = 0[/math]
[math] 4x_1 + -6x_2 = 0[/math]
[math] -4x_1 + 6x_2 = 0[/math]

Or equivalently, if A1 is the left column of A, and A2 the right column, [math] x_1A_1 + x_2A_2 = 0[/math]. Therefore, [math] x_1A_1 [/math] must cancel out [math] x_2A_2 [/math] for that equality to hold. Your solution works, since if x1 = 1.5 & x2 = 1, every one of the above equations works out.

The 1 is there since the system is underdetermined, and you need to set x2 to some nonzero value (otherwise you get the trivial solution). Setting x2 to 1 is a good choice, since it makes finding x1 from any of the above equations pretty easy. Does that make sense?

[Anonymous No.12765787]

Small question: I want to brush up on regular college algebra, which book is better; algebra for college students by Kaufmann or algebra and trigonometry by Sullivan ? I haven’t read any of those. Just asking in case someone knows them.

[Anonymous No.12765789]

>>12765774
I
I-I thought it was constants and not x_2...
Thank you anon, it makes a lot more sense now... I really appreciate it and I wish you good rolls...

[Anonymous No.12766038]

>>12765272
Yes I missed the /2
I used 32 and 62 for rho and g I think
Did you get it?

[Anonymous No.12766453]

What's the name of the operation of trying to express a number as a percentage of a second number

[Anonymous No.12766548]

Anybody has any idea how can i discribe a scalar field with a delta interaction term coupled to the field squared, such as: [math]\mathcal{L} = \frac{1}{2} \left[ (\partial _t \phi)^2 - (\partial _x \phi )^2 - m^2 \phi ^2 - \delta (t) \delta (x)\phi ^2 \right] [/math] The propagator cannot be defined cause the billinear part of the lagrangian is not invertible. I thought that maybe i can treat this somehow perturbativelly, adding a coupling λ to the interaction, but i get all sorts of divergences (even if i smooth out the deltas with some gaussians and then take the limit). So the solution is typical free klein gordon waves for (t,x)≠(0,0) and thats that? What happens at the origin at time =0? (some kind of source maybe? but its coupled to [math] \phi ^2[/math]) Can't i write a complete global solution that produces the EoM? any help appreciated

[Anonymous No.12766766]

Should I try applying to German Universities with DAAD scholarships (or government scholarships here if DAAD does not accept me)? I'm from a third-world country with no research experience yet, but I plan to re-contact some labs here after this quarantine. Or should I do my Master's here instead?
I'm an undergraduate in CS, though I plan to pursue something heavy in maths but still grounded with applications since I don't want to stay poor.

[Anonymous No.12766812]

how do i find the height h?
i tried to encompass the circles in a triangle and then i thought that the required height is the height of the triangle, and then use the center of mass of the triangle

this is the only question in the test that i didn't know how to do :|

[Anonymous No.12766833]

>>12766812
Draw a triangle from the circles' centers, calculate its height and add 2r

[Anonymous No.12766837]

>>12766833
could you explain why I have to do it this way? i don't get why i have to draw a circle from the centers and not how i did it

[Anonymous No.12766867]

>>12766837
>could you explain why I have to do it this way
You don't have to, I'm sure there's other ways that work.

[Anonymous No.12766971]

has /sci/ got a probability flowchart I can follow?

what should I do to go from beg to advanced?

[Anonymous No.12766987]

>>12766971
(samefag)
i found the /sci/ road to riches chart. Is that good? Some of these charts are autistic as fuck /sci/.

[Anonymous No.12766991]

in the equation to calculate the delta of y in relation to gravity, why is time (t) squared, and why is gravity (g) halved?

[Anonymous No.12766998]

>>12766987
> Is that good?
No, it's a meme.
Roughly speaking, you'll want to read an undergrad level probability book, then you'll want to learn real analysis, then you'll want to learn grad level probability, and then it branches out a lot, but you'll want to at least read up on stochastic processes, Markov chains and asymptotic analysis.

[Anonymous No.12767003]

>>12766991
[math]\frac{d^2y}{dt^2} = g[/math]

[Anonymous No.12767010]

>>12766998
many thanks anon

[Anonymous No.12767033]

>>12763573
they did all this on their golden probe with the whore and the cumbrain on it

[Anonymous No.12767166]

>>12765237
https://en.wikipedia.org/wiki/Captain_Midnight_broadcast_signal_intrusion

[Anonymous No.12767171]

>>12766453
factorization

[Anonymous No.12767187]

>take ssri for a few months
>no to very minor improvement
>try quitting because i start to wake up for a two three times per night, usually just before 5 am
>sleep is still fucked, hot flashes, it starts twitching deep in my head when trying to move head and eyeballs to either direction
what gives? am i too biologically inferior to even take ssris?

[Anonymous No.12767270]

>>12762298
i hate using google scholar because i end up finding a 20 page long article and i have to skim through the entire thing just to find the number. isn't there any database just for constants?

[Anonymous No.12767292]

>>12766453
Percentage ratio.

[Anonymous No.12767549]

>>12767187
stop using drugs

[Anonymous No.12767930]

>>12767187
talk to your psychiatrist you dumb fuck

[Anonymous No.12767983]

>>12766038
Yep. Thanks again anon.

[Anonymous No.12768267]

How good is the calculus review section of Griffith's E&M book? My vector calc is terrible. I trust the review would be good enough to get me through the book, but would it be a good enough substitute for actually relearning vector calc?

[Anonymous No.12768676]

Why do electronics act all fucky if they're left on for too long? Why does turning them off and on again work?

[Anonymous No.12768699]

Can someone please tell me how they got 2 theta? And why they chose cos and not sin or any other trig function? Sorry...

[Anonymous No.12768787]

>>12768699
>2 theta
Conduction begins at theta and ends at pi-theta
The entire area in which it conducts is therefore 2theta
>why they chose cos and not sin
Don't know, there should be a definition prior to that task.
Doesn't really make a difference though, sin is just cos with an additional phase and vice versa.

[Anonymous No.12768802]

>>12768699
What they're trying to do is find the part of your 24V sinusoid that lies above 12V. Using cosine makes it easy since then your peak is centered at 0. This way, you just need to find [math] \theta_0 [/math] such that [math] 24\cos(\theta_0) = 12 [/math], since that will tell you that your sinusoid is greater than 12V when [math] \theta \in (-\theta_0, \theta_0) [/math], and that interval has a length of 2theta_0.

You could also solve this using a sine, but it's a little uglier since you're peak is centered at 90, not 0.

[Anonymous No.12768857]

>>12768787
...W-what?
Sorry, in previous classes for circuit analysis, we never had to deal with sinusoidal waves which is why I don't get what's going on... Is it like dis? I think I 100% fucked it up somewhere
>>12768802
>What they're trying to do is find the part of your 24V sinusoid that lies above 12V.
Okay this part makes senese!
>Using cosine makes it easy since then your peak is centered at 0
Uhh, wat
>interval has a length of 2theta_0.
Okay I think(?) I get why it's 2 theta now, because it goes from -theta_0 to +theta_0, but where is theta_0 at

Sorry, this is the first time I've seen this type of problem, as well as one using waves so I'm kind of mindfucked

[Anonymous No.12768895]

If we slice through a surface f(x, y) with a plane that is either perpendicular to the
x-axis or perpendicular to the y-axis, then the resulting intersection is a curve, which is called
a ___ of f(x,y)

Cross section or level curve?

[Anonymous No.12768930]

>>12768857
The zero angle is the peak of the wave. Conduction is symmetric about that point, i.e. over the interval [-θ,θ]. At the start of the interval you have 24cos(-θ)=12, at the end you have 24cos(θ)=12. cos is even, i.e. cos(-x)=cos(x), which is why they chose to use cos rather than sin.

[Anonymous No.12768945]

>>12768930
Ohhh I think I get what you mean. It starts at the Y-intercept here, and then it cycles through to 2pi.
Using intervals rather than pi is kind of weird though. Thank you anon.

[Anonymous No.12768959]

>>12753493
i think 95 iq must be sad

[Anonymous No.12768987]

Give an example of a function of 3 variables whose family of level surfaces is a collection of evenly spaced planes, which are parallel to the yz-plane

[Anonymous No.12769029]

>>12756908
>doesn't have an easily found inverse transform.
every time i think ill solve an improper integral with laplace -_-

[Anonymous No.12769091]

>>12768895
Cross-section. A level curve is obtained from a plane parallel to both the x and y axes, i.e. f(x,y)=k.

>>12768987
f(x,y,z)=kx

[Anonymous No.12769103]

>>12769091
Thanks m8 I figured them both out but it's nice to have confirmation.

[Anonymous No.12769232]

The plane z = 5x − 9y + 10 is the level surface g(x, y, z) = 2 of the
function g(x, y, z) when g(x, y, z) = ?

[Anonymous No.12769240]

>>12769232
We start with [math]z = 5x - 9y + 10[/math], pass z to the other side for [math]0 = 5x-9y-z+10[/math], and then we add 2 to both sides for [math]2 = 5x - 9y - z + 12[/math]. The thingy on the right is a (candidate for) g.

[Anonymous No.12769254]

>>12769240
So it's just the original function?

[Anonymous No.12769262]

>>12769254
Your question honestly doesn't make sense.

[Anonymous No.12769266]

>>12769262
Sorry, it's been a long week and I'm running on fumes

[Anonymous No.12769277]

>>12769266
ah, g(x,y,z)= 5x-9y-z+12
We take the plane equation and find the correct c value so g(x,y,z)=2
Am retarded, thanks

[Anonymous No.12769368]

Can current come OUT of ground? Can current flow INTO ground? Doing some assumptions in circuit analysis and I'm getting a bunch of weird results.

[Anonymous No.12769429]

>>12769368
Ignoring static charge, KCL says that the total current entering or leaving any node is zero. So current can only come out if the same current goes in.

[Anonymous No.12769881]

>>12769368
Yes, current can come out of ground or into it. Any normal AC circuit does this, even conventionally

[Anonymous No.12769912]

I found this slide in one of my old lecture notes and I remember not understanding it then.

I think that the answer is A because the force vector is in the direction of the distance traveled. I thought the answer would be B IF the force vector was in the direction of the floor.

I never found out the answer but even though I think I'm correct, the poll results make me question it. Thoughts?

[Anonymous No.12769924]

>>12769912
I meant to say IF the direction traveled was parallel to the floor, ie there was no ramp but the force applied was still not parallel to the floor.

[Anonymous No.12769938]

>>12769912
1. Work is the dot product of the force vector and the displacement vector. The dot product of these two as illustrated would simplify to just Fd

[Anonymous No.12770451]

thread for cool /sci/ sites: >>12770243

[Anonymous No.12770502]

>>12770451
her hair doesn't make sense

[Anonymous No.12771051]

Can anybody explain to me why, in the part I highlighted in pic related, [math]|b_n - b| < \frac{|b|}{2} \implies |b_n| > \frac{|b|}{2}[/math]
I intuitively understand why it works, but I cannot come up with anything rigorous.

[Anonymous No.12771107]

What does it mean if I only understand sciences when explained through numbers and don't get it at all when it's explained through words/letters or goes too abstract? I'm trying to choose a major, but a lot of them probably requires stuff I don't get (physics in general and some math stuff like limits) or/and demand to be more concerned with explaining how something works or what causes X thing instead of just getting clear, definitive result preferably expressed solely in numbers and moving on to another on

[Anonymous No.12771116]

>>12771051
|b_n-b|<0 -> |b_n|< |b|
-|b_n-b| < |b|/2 -> -|b_n| < |b|/2 - |b| = -|b|/2
-> |b_n| > |b|/2

|b_n-b|>0 shows |b_n| < 3/2 |b|

[Anonymous No.12771124]

>>12771116
I came up with the second line but I missed that you could put a minus sign at the very beginning, so the end result didn't make much sense to me. Thanks a lot!

[Anonymous No.12771130]

>>12771051
use |x| - |y| < |x+y| < |x| + |y| in some way

[Anonymous No.12771283]

Any book recs for the history of numerology? all the ones I've found are presenting numerology as something that is real i.e change your life by writing these numbers and shite like that what I'm after is just a history of numerology without presenting it as a real thing

[Anonymous No.12771466]

Is there a way to differentiate a fart and a 'fart'? /sqt/bros, please help. For the first time in YEARS, I shat myself while trying to fart.

[Anonymous No.12771527]

Why isn't there a earth science general on this board.
Loads of volcanoes and quake shit going on.

[Anonymous No.12771537]

>>12771527
You can make one if you wanted to anon, people occasionally make new generals/revive old ones like the stem career general.

[Anonymous No.12771582]

Java

I'm a beginner, trying to create a loop do while.
Do keep asking for the number 1-12, as long as the (while) number isn't 1-12.

It only repeats if I set while(numb> 1 && numb<12)


Also whats the best forum to get quick answer about coding?

[Anonymous No.12771586]

>>12756531
>Introd. to Lasers
cool

[Anonymous No.12771824]

>>12768267
I found it to be good enough. If youre going to be tackling problems specific to vector calc then you need to relearn but to get by its does its job.

[Anonymous No.12771832]

>>12765275
Its really intuitive and easy anon, I keep a notepad file where I have most of the stuff i use, inserting pictures, tables ect. That i can just copy and paste over and modify to suit the situation. The amsmath package makes writing very equation orientated reports much nicer.

[Anonymous No.12772001]

How much should I be concerned for mercury content in canned tuna? I used to eat sandwiches with tuna every day as a child
Am I gonna make it?

[Anonymous No.12772005]

>>12771051
The Abbott is such a fucking BASED book.

anyway

[math]||b_n|-|b||\leq|b_n-b|<\frac{|b|}{2}[/math]
[math]||b_n|-|b||=||b|-|b_n||<\frac{|b|}{2} \Rightarrow -\frac{|b|}{2}<|b|-|b_n|<\frac{|b|}{2}[/math]
[math]|b_n|>|b|-\frac{|b|}{2}=\frac{|b|}{2}[/math]

[Anonymous No.12772247]

Any europeans know good universities for optics/lasers/photonics for a phd? only ones ive heard of are KIT and Abbe school of photonics.
Im assuming oxford and cambridge have some sort of program for it but havent looked into it yet.

[Anonymous No.12772365]

Dumb question time.
I'm trying to do some diode circuit analysis, the blue is the constant voltage drop model where I assumed that the diodes were on so they turn into a 0.7V source. My question is about the parallel arrangement you see at red (1) and (2).
I can see why it went from 5.0V to 3.3V as there is a voltage drop across the 1.7K resistor on the top line but I don't understand why we needed to subtract the two voltage sources on the bottom line (0.7V and 1.0V) rather than add them.
I know this is probably some basic circuit analysis stuff, however, my teacher wasn't really the best (espescially during zoom university) so uhh, pretty lost here...

[Anonymous No.12772390]

>>12772365
Look at how the + & - are defined for your two voltage sources on the lower path. Going from from node 1 to node 2, you're going from + to - across those sources, and so you're going down 0.7V and then 1V when you travel along that path.

[Anonymous No.12772410]

>>12772390
Ohhh, I think I get what you're saying. The bottom voltage sources (0.7 and 1.0) are + -> -, meaning that they go through a drop of 0.7 and 1.0 respectively when going across them, had they been - -> +, they would've gone through a gain of 1.7 instead. Thank you anon!

[Anonymous No.12772528]

any of you guys have any luck with nicotine as a study aid?

[Anonymous No.12772921]

>>12772005
>The Abbott is such a fucking BASED book.
it really is! thanks for the detailed alternative answer, using the reverse triangle inequality was my first idea but I couldn't get even one step beyond that.

[Anonymous No.12773048]

Can anyone show me how to solve this ODE by hand?

Everything except y(t) is a constant

[math] \frac{\lambda}{y(t)} \ \frac{\delta y(t)}{\delta t} = (\frac{k \ M}{2 \ \pi}-Z) [/math]

[Anonymous No.12773107]

>>12773048
What function is a scalar times itself when you take a derivative of it?

[Anonymous No.12773138]

>>12773048
Rearrange to get the equation in the form [math]\dfrac{dy}{dt} = ay(t)[/math] where a is some constant. So it should be trivial to see that [math]y = e^{ay}[/math].

[Anonymous No.12773140]

Is it possible that I am bad at math because I skipped at least 50% of classes starting from grade 5, never did homework and never tried to learn anything mathematical other than in pursuits of other interests?

[Anonymous No.12773154]

>>12773140
How would we know? You could be good at math but lack the education or just a lazy idiot.

[Anonymous No.12773160]

>>12773107
The exponential function.

I mean, I guess the solution is:

[math] y(t) = e^{((\frac{\Omega \ M}{2 \ \pi \ L}-\frac{R}{L}) \ t )} [/math]

Because:

[math]\frac{\delta \ e^{((\frac{\Omega \ M}{2 \ \pi \ L}-\frac{R}{L}) \ t )}}{\delta \ t} = (\frac{K \ M}{2 \ \pi}-Z) [/math]

So [math] \frac{\delta \ e^{((\frac{\Omega \ M}{2 \ \pi \ L}-\frac{R}{L}) \ t )}}{\delta \ t} \ e^{((\frac{\Omega \ M}{2 \ \pi \ L}-\frac{R}{L}) \ t )} = (\frac{K \ M}{2 \ \pi}-Z) [/math]

is the solution.

But is this the correct way of doing it? i.e. just being able to "see" that it is the exponential function

[Anonymous No.12773165]

>>12773160
>But is this the correct way of doing it? i.e. just being able to "see" that it is the exponential function
yep, theres no ez method for solving differential equations

[Anonymous No.12773192]

>>12773165
Thanks man
What about the constant though? I mean when I solve the ODE with no boundary or initial conditions there should be an unknown constant c in the solution right, because it comes from an integral.

But how do I add this constant c to my solution when I haven't actually integrated anything?

Can I just say:

[math] y(t) = e^{((\frac{K \ M}{2 \ \pi \ \lambda}-\frac{R}{\lambda}) \ t)} + c_1[/math]

[Anonymous No.12773227]

>>12773192
it's a linear combination of the solutions, i.e. you multiple the function by the constant, i.e. ce^(...)

[Anonymous No.12773251]

>>12773154
But everyone on /sci/ claims to be a math genius despite never even having seen a number before.

[Anonymous No.12773253]

>>12773227
Thanks

[Anonymous No.12773284]

>>12773048
Your equation can be reduced entirely in
[math] \frac{dy(t)}{y(t)}=\alpha dt [/math]
Integrate in time both sides
[math] \int_{t_0}^t\frac{dy(t)}{y(t)}=\alpha(t-t_0)[/math]
You obtain by using usual rules
[math] \ln(y(t))-\ln(y(t_0))=\alpha(t-t_0) [/math]
By rearranging
[math]y(t)=y(t_0)e^{\alpha(t-t_0)}[/math]

[Anonymous No.12773289]

>>12773284
*[math] y(t)=y(t_0)e^{\alpha(t-t_0)} [/math]

[Anonymous No.12773299]

>>12773284
As you see I didn't guess shit. The guesswork in differential equations comes up in more difficult situations, like ansatzes for PDEs

[Anonymous No.12773331]

How do I determine the strongest asymptotic relationship between sqrt(log(n)) and n/(2^log(logn))

[Anonymous No.12773359]

>>12773299
>I didn't guess shit.
you performed an integral, all you did was move the step where you have to know "the usual rules"

[Anonymous No.12773371]

>>12773359
bro usual rules means integration by substitution

[Anonymous No.12773733]

>>12773359
However you do it, you have to know certain derivatives or integrals. But using separation of variables and integration gives you *the* solution, whereas a guess only gives you *a* solution. Knowing that d/dt e^kt = ke^kt gives you a solution, but how do you know that's the only solution?

If the question involved a second-order linear ODE, you might try ce^kt and discover that was a solution. But while it might be apparent that there are (usually) two possible values of k (obtained as the roots of a quadratic), it might be less obvious that a solution for specific initial values typically requires a weighted sum of both solutions, of the form c1e^k1t+c2e^k2t. And worse, if the quadratic has a repeated root (a single value of k), the actual solution involves a te^kt term. If you didn't think to guess that, you'll end up trying to find a single value of c which makes ce^kt match both initial values (y(0) and y'(0)) and that isn't going to happen (unless y'(0)=ky(0)).

[Anonymous No.12773755]

Do linewidth Broadening cause mode splitting in EM-wave reflections?

[Anonymous No.12773785]

How do I do this limit

[Anonymous No.12773794]

>>12773785
Looks like an indeter form pf inf/inf, I'd try l"hobitals but intuition tells me itll be infninity as 2^x grows much faster than x

[Anonymous No.12773800]

>>12773794
The limit is already "solved" though, I presume it's asking you to prove the result, assuming it's correct

[Anonymous No.12773803]

>>12773785
simplify the exponential term to start, then l'hopital's rule should make it clear.

[Anonymous No.12773809]

>>12773803
Not sure how to simply the exponential

[Anonymous No.12773817]

>>12773809
Use the change of base formula to make the outer log into log_(base 2). Can you see where to go from there?

[Anonymous No.12773831]

>>12773817
No, I changed it log_2(log_10(x))/log_2(10) but I'm still stuck on where to go

[Anonymous No.12773859]

>>12773733
thanks anon, i like your post

[Anonymous No.12773872]

how do I prove that a certain set has empty interior? I'm trying to prove that a certain finite-dimension subspace of a vector space is nowhere dense. Clearly, every finite-dimensional subspace is closed so it just amounts to proving that the subspace itself has empty interior but I don't really know what to do.

[Anonymous No.12773878]

>>12773831
No problem! Recall that for all [math] x, y > 0, y^{\log_y(x)} = x. [/math] Then, using your expression for the argument of the exponential, we see that this limit simplifies to [eqn]\lim_{x \to \infty} \frac{\log_{10}(x)^{\frac{1}{\log_2(10)}} \log_{10}(x)^{\frac{1}{2}} }{x}. [/eqn] From here you should be able to make an argument using L'hopital's rule that the limit goes to 0. I might recommend comparing it to a similar limit, but which has an integer power of the logs in the numerator to make things a bit easier for your notation and math.

[Anonymous No.12773966]

>>12773831
>>12773878
I seriously doubt the question is log_10. log_e is commonly written as both log or ln in math textbooks or courses. But anyway ...

[math]
\begin{align}
y &= 2^{\log(\log{x})} \\
\log{y} &= \log(\log{x}) \log{2} \\
\log{y} &= \log(\log^{\log{2}}{x}) \\
y &= \log^{\log{2}}{x}
\end{align}
[/math]

So
[math]
\begin{align}
&\frac{ 2^{\log(\log{x})} \log^{1/2}{x}}{x} \\
= &\frac{ \log^{\log{2}}{x} \log^{1/2}{x}}{x} \\
= &\frac{ \log^{\log(2) + 1/2}{x} }{x} \\
= &\frac{ \log^{a}{x} }{x}
\end{align}
[/math]

and you should be able to do the rest from there.

[Mohan No.12774002]

>>12773785
well, the derivative is
((2log2+1 )/xlogx - 1/x) times the function it's self.
the limit n to inf for the derivative is zero, showing a convergence.
now it's as hard as it was to solve.

[Anonymous No.12774287]

I'm trying to do problem 4.72, but I'm having trouble. The current proof I have relies on, in the case of the mapping cylinder, relies on [math] i_{0} \simeq i_{1} [/math] , but I'm having trouble proving that and finding some other method.

[Anonymous No.12774292]

>>12773785
Put x=e^u and you get e^((log(2)+1/2)log(u)-u).

[Anonymous No.12774558]

How do i solve [eqn]a_0 cos(a_1 - a_2) = a_3 cos(a_1 - x)[/eqn] ive been trying for hours now.

[Anonymous No.12774590]

>>12774558
-acos(a_0/a_3 cos(a_1-a_2))+a_1?

[Anonymous No.12774703]

>>12773140
Well I sucked super hard at maths in school and am about to wrap up a comp sci degree, I know that's not the pinnacle of mathematical achievement but there was a lot of maths that I had to work really hard to understand. So even if you
>skipped at least 50% of classes starting from grade 5, never did homework and never tried to learn anything mathematical other than in pursuits of other interests?
you can still get better.
Although maybe that was not even what your question was getting at and I'm just rambling.

[Anonymous No.12774749]

>got my HIDA scan back
>ejection fraction of 18%
am I dead?

[Anonymous No.12774759]

>>12773872
You may look into proving that if we assume an element belongs to the interior, and we show that necessarily its open neighborhood always intersects the exterior set, then it is not an interior point and by contradiction there are no elements in the interior. This is just an option though

[Anonymous No.12774903]

Find the upperbound for the recurrence relation T(n) = 2T(n/2) + 2. The multiplication by 2 is confusing me, I thought it;s just log_2

[Anonymous No.12774965]

What should I study with 110IQ ?
Interested in engineering, technology

[Anonymous No.12774976]

>>12774965
It's lower than the average college grad, so you will need tremendous effort to graduate from an engy program. Not impossible, and it would be a way to overcome the shame of your low IQ (I'm a midwit too so I understand). You need time and strong determination. You can do it anon.

[Anonymous No.12775016]

>>12774976
Yikes
I thought about Industrial Engineering (its a Mix of Business and engineering in my country, Most people said its easier than a pure engineering degree)

[Anonymous No.12775028]

>>12775016
Don't know about your country but in mine industrial engineering is frowned upon as a scam program which requires considerably more effort than a business/econ degree but does not provide much more opportunities career-wise nor it teaches you much more.

[Anonymous No.12775086]

>>12772247
in france, there is grenoble, and paris and orsay
https://www-liphy.univ-grenoble-alpes.fr/pagesperso/pique/research.html

[Anonymous No.12775088]

>>12773331
limited development with big O and small O ?

[Anonymous No.12775089]

>>12774965
>>12774976
Isn't iq a meme (in terms of actual intelligence), because as far I'm aware it only has proper correlation with life standard + possible job occupation?

[Anonymous No.12775110]

>>12775086
>https://www-liphy.univ-grenoble-alpes.fr/pagesperso/pique/research.html

https://www-liphy.univ-grenoble-alpes.fr/Membres-de-l-equipe-1403?lang=fr

https://www-liphy.univ-grenoble-alpes.fr/LAsers-Molecules-et-Environnement-1216?lang=fr


Orsay has even a M2 in photonics so they have phds


http://www.ismo.universite-paris-saclay.fr/spip.php?rubrique3&lang=fr

https://master-omp.com/propositions-de-theses/


paris-orsay is more famous than grenoble

[Anonymous No.12775146]

>>12775089
no idea, when i was 16 i did an intelligence test with psychologist ( I was also slighty depressed)
>>12775028
germany

[Anonymous No.12775160]

Will the future of humanity resurrect all sentient life in a heaven simulation?

[Anonymous No.12775203]

>>12774903
> Find the upperbound for the recurrence relation T(n) = 2T(n/2) + 2.
If n is a power of two, you have T(n)=(T(1)+2)n-2.

Putting U(k)=T(2^k)
=> U(k) = T(2^k)
= 2T((2^k)/2)+2
= 2T(2^(k-1))+2
= 2U(k-1)+2

In matrix form:
[eqn]
\begin{align}
\begin{pmatrix}U_k \\ 1\end{pmatrix}
& = \begin{pmatrix}2 & 2 \\ 0 & 1\end{pmatrix}
\begin{pmatrix}U_{k-1} \\ 1\end{pmatrix}
\\
& = \begin{pmatrix}2 & 2 \\ 0 & 1\end{pmatrix}^k
\begin{pmatrix}U_0 \\ 1\end{pmatrix}
\\
& = \begin{pmatrix}1 & 1 \\ -{\frac 1 2} & 0\end{pmatrix}
\begin{pmatrix}1 & 0 \\ 0 & 2\end{pmatrix}^k
\begin{pmatrix}0 & -2 \\ 1 & 2\end{pmatrix}
\begin{pmatrix}U_0 \\ 1\end{pmatrix}
\\
& = \begin{pmatrix}1 & 1 \\ -{\frac 1 2} & 0\end{pmatrix}
\begin{pmatrix}1^k & 0 \\ 0 & 2^k\end{pmatrix}
\begin{pmatrix}0 & -2 \\ 1 & 2\end{pmatrix}
\begin{pmatrix}U_0 \\ 1\end{pmatrix}
\\
& = \begin{pmatrix}2^k & 2^{k+1}-2 \\ 0 & 1 \end{pmatrix}
\begin{pmatrix}U_0 \\ 1\end{pmatrix}
\\
& = \begin{pmatrix}(U_0+2) 2^k - 2 \\ 1\end{pmatrix}
\end{align}
[/eqn]

=> U(k) = (U(0)+2) 2^k - 2
=> T(2^k)= (T(1)+2) 2^k - 2
=> T(n) = (T(1)+2) n - 2

For a more general solution, you need to specify a base case, e.g. the value of T(n) for 1/2<n<=1.

[Anonymous No.12775209]

>>12775089
Eh, sadly not. IQ tests are seriously flawed and can be learned, but like standardized tests they provide good measures of your baseline mental horsepower in the first tries. Low intelligence people and midwits are not inferior, they just need time to learn, adjust and optimize to perform like high intelligence people, and their performance caps out after enough training. High intelligence people can adapt more easily to new tasks, can do more things and better, and require little to no training for new tasks.

[Anonymous No.12775503]

>>12774590
I'm hoping theres a way to reduce this even further using trig identitites. since if a_0=a_3 then it reduces rather nicely to a odd integer recurrence. [eqn]acos(\frac{a_0}{a_3} cos(a_1 - a_2)+2\pi n)[/eqn] isn't very nice.

[Anonymous No.12775645]

How do I solve linear modular equations when there is x and y?
10x ≡ 15(mod 17),
3y≡3(mod17)

[Anonymous No.12775655]

>>12775645
Each of those equations only has one variable, so you just solve them individually. Did you mean to pick a different example (simultaneous equations)?

[Anonymous No.12775670]

>>12775645
Also: the second one is utterly trivial.

[Anonymous No.12775682]

>>12775645
If
[math] 10 x \cong 15 \mod 17[/math] then [math]2 x \cong 3 \mod 17[/math].
Solving that is trivial.
(Hint: it's 10.)

[Anonymous No.12776129]

My dumb question is:
Can you tell me to get off my ass and study, please

[Anonymous No.12776156]

can atomic bonds break in compression and additionally can 2 atoms have overlapping electron clouds without being bonded?

[Anonymous No.12776182]

>>12776129
Get off your ass and study, anon! You can't get anywhere if you don't start moving!

[Anonymous No.12776202]

Circuitbros, I have a question about current. Why is it that a current passing through a series resistor has the 'same current' at each point? Would the resistor not affect the current at all like it does for voltage? Sorry for the poor drawing, hard to draw on the mouse but I tried to describe what I meant

[Anonymous No.12776227]

>>12776202
current is the amount of charge (electrons) passing through an area (cross-section of wire) in a given period of time (1 amp = 1 colomb per second). think of it like water in a hose: if x amount of water is entering the hose, how much must be leaving it? does your answer change if you put your thumb over the nozzle?

[Anonymous No.12776245]

>>12776227
>if x amount of water is entering the hose, how much must be leaving it?
x amount must be leaving... right...?
>does your answer change if you put your thumb over the nozzle?
i dont think so, though if too much water is supplied and i have mega strong thumb, maybe the hose will break... oooh, that's kind of like how components melt and stuff!
thank you anon, I think I get it now!

[Anonymous No.12776265]

>>12776245
>x amount must be leaving... right...?
right, because otherwise where did the water go?
KCL or whatev its called is essentially just conservation of matter: if some amount of current is entering a point, node, etc., then that much current must be leaving that point as well. this is always true in circuit analysis no matter how you draw your boundaries, you can circle half the circuit and this equality still holds

[Anonymous No.12776286]

I hope this threard doesnt die b4 i get a reply.
Ihave the vvariable X of uniform distribution in (a,b) that simulates the distribution od juice in oranges, that are used to fill bottles of a volume=15a. The Bottles are considered full when they are m=98% full or more. What's the distribution of V, the volume found in the bottles?
I have no clue but obviously the mean is 99%*15a. What do you say? Some aproximation?

[Anonymous No.12776289]

>>12776265
Thank you anon!
Yeah I keep forgetting that they're conservation of matter! Same for KVL or something I think, but for energy...

[Anonymous No.12776312]

>>12776286
Let me see if I understood the problem:
You have a bunch of oranges and a bunch of bottles. You pick up a bottle and start filling it with orange juice. If the bottle is past 98% capacity and the orange you're currently squeezing is done, you close the bottle and pick up a new one. If the orange you're squeezing is still going, but the bottle is at max capacity, you close the bottle and squeeze the rest of the juice still on the orange into the next bottle.

Honestly a pain in the ass to estimate and the qualitative behavior depends on both the 98% and the (a, b), just do Monte Carlo.

[Anonymous No.12776404]

For the constant voltage drop model for diode, the V(anode) - V(cathode) must be greater than 0.7V (assuming that we're using 0.7V as the turn-on voltage), and not greater than OR equal to right?

[Anonymous No.12776476]

>>12776312
it's ike this.
you squeze one orange and you put the juice of an orange at the time untill the bottle is 98% full or more. if it gets 100% the rest of the juice form that orange is trown away (overflows)

[Anonymous No.12776497]

Quick, is a first order differential circuit a circuit with either capacitor or inductor, and a second order differential circuit is a circuit with both of them?

[Anonymous No.12776750]

>>12776497
yeah

[Anonymous No.12776844]

Hey, brainlet here.

I have a probability problem. It's about a video game dropping an item. Each time you loot a treasure chest, you have a chance for it to be this epic item.
Let's say it takes an average of 8 hours to get the item to successfully drop, and you get 1 treasure chest to open per minute.
Now, what are the chances of getting the item?
What is the standard deviation?(that's to the 86% percentile right?) And what is the second standard deviation?(that's to the 98% percentile right?)

[Anonymous No.12776894]

>>12776844
that's pretty much just a binomial distribution

[Anonymous No.12777023]

Guys java Beginner here.

I can choose 3 options. (Switch)
1. $ earned. (Input)
2.$ spent (input)
3. Board that shows total amount of $earned and $spent.

I created a switch with 3 cases but I don't know how to call the variable for the total of $spent and earned so I can show it inside case 3 and calculate stuff.

Any help please, I really want to finish this shit

[Anonymous No.12777026]

>>12776844
not sure about the 86% or 98% percentile, but if you think of your item drop as dice rolls and work backwards you can get your answer.
6 sided dice. 1/6 chance of rolling the number you want, the average number of rolls to get a specific number is 1/(1/6) = 6. So in your case we have the average number of attempts (1/min so in 8 hours you perform 480 rolls) and you can do
1/x = 480
x = 1/480
x ~= 0.2% chance

[Anonymous No.12777036]

>>12777023
post code. it's possible you are misusing switch cases

[Anonymous No.12777052]

>>12776844
>>12776844
Problem looks strange. Lemme have a try.
We have that the average time between events is 8 hours. We open chests every minute, so we can assume that we try in approximately continuous time. So the time between events is an exponential distribution with mean (in hours) [math] 8 = 1/\lambda[/math] which implies [math] \lambda = 1/8 [/math]. The standard deviation is [math]1/\lambda=8[/math] hours and the variance is [math]1/\lambda^2=64[/math] hours. The probability of getting the item, for example, in less than one hour is [math]1-e^{\lambda} \approx 0.12[/math].

[Anonymous No.12777061]

>>12777023
>>12777036
oh nevermind, you need to learn about scope. you defined spent and earned inside your case block so you can't access it from the other blocks. just create a local variable inside your main function and update the parameter inside your case so that it's always visible to all cases e.g.


int earned = 0;
int spent = 0;

switch (var) {
case "earned":
earned = input ...
break
etc
}


[Anonymous No.12777082]

>>12776844
my answer here is not very different from >>12777026 in its result: indeed the probability of getting the item in one minute or less is [math]1-e^{-\frac{1}{8}\frac{1}{60}} \approx 0.002 = 0.2%[/math]

[Anonymous No.12777085]

>>12777082
0.2 percent obviously. Also here >>12777052
is a typo [math]1-e^{-\lambda} \approx 0.12[/math]

[Anonymous No.12777206]

>>12777052
Sorry if I don't know much about probability, but how would you differentiate poor luck? As in, 12% of the time it takes 16 hours?

[Anonymous No.12777224]

Thread almost ded
Just want to say that I really appreciate you guys. I never really learned how to ask for help for 21 years and somehow didn't fail out of college (but did get downright atrocious 2.5-2.9 GPA), now my GPA's decent enough that I'm not ashamed of it.

[Anonymous No.12777296]

>>12777224
/sci/ is a slow board, it probably still has ~4 hours left.

[Anonymous No.12777301]

>>12777296
Fuck.

[Anonymous No.12777311]

>>12777301
You can always just bump garbage on the catalog to make it die faster.

[Anonymous No.12777328]

>>12777311
That'll be mean to the other threads :(

[Anonymous No.12777380]

>>12777206
what do you mean by poor luck?

[Anonymous No.12777393]

>>12776404
Pick your poison. It's a shitty model so I wouldn't get but picky if 0.7 is included or not.

[Anonymous No.12777394]

NEW BREAD >>12777391