/sqt/ Stupid Questions Thread

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/sqt/ Stupid Questions Thread Anonymous Sat Jan 20 10:52:35 2018 No.9450832 [Reply] [Original]

This thread is for questions that don't deserve their own thread.

Tips!
>give context
>describe your thought process if you're stuck
>try wolframalpha.com and stackexchange.com
>How To Ask Questions The Smart Way http://www.catb.org/~esr/faqs/smart-questions.html

Previous thread >>9442805

>>	Anonymous Sat Jan 20 11:24:13 2018 No.9450874 Hey, can someone suggest a good book to learn Power series from? I'm an undergrad and i would really like to know how to find the values of many series. Please suggest some sources. Thank you!

>>	Anonymous Sat Jan 20 11:26:35 2018 No.9450878 >>9450874 you're not going to find a book on just power series, or just series for that matter. the princeton "cracking the math GRE" book has a good section on series and sequences

>>	Anonymous Sat Jan 20 11:39:31 2018 No.9450896 what's a good book to give me an intuitive understanding of calculus? preferably something that isn't 1500 pages

>>	Anonymous Sat Jan 20 12:44:52 2018 No.9450972 Does [math]\displaystyle \mathbf{F} = \frac{ \mathrm{d} \mathbf{p} } { \mathrm{d} t}[/math] still hold in non-inertial reference frames?

Anonymous Sat Jan 20 12:47:05 2018 No.9450975

Show that if [math]x \in \mathbb{R}[/math] and [math]0 < x < 4[/math], then [math]\frac{4}{x(4-x)} \geq 1[/math].

The easiest way is to show this by cases right? Doing it when x = 2 is easy, but I have no idea what to do when x < 2 and when x > 2. Like I get that that the denominator will be the greatest when x = 2 and smaller for all other values within 4, but I don't know how to show it.

Anonymous Sat Jan 20 13:00:17 2018 No.9451002
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Conceptually speaking, in what way is an integral an "anti derivative"?

As I understand it, derivatives are changes of one property with respect to another calculated by tiny points converging to a particular point. Integrals are the combination of tiny points. How does that make them inverse?

>>	Anonymous Sat Jan 20 13:04:15 2018 No.9451014 How do you guys get jobs in a field outside your degree? I just got an email from my school saying there's openings for a bank, but I'm in engineering, and I think I would fuck something up for the company if I managed to get hired.

Anonymous Sat Jan 20 13:10:55 2018 No.9451026

>>9451014
What exactly is your question?

Engineers probably know enough math to work at a bank. More than theyd need really. What position is it for?

As to how, you apply for the job and write a brief statement that tells them you believe your education and knowledge could be beneficial for the position despite not being a finance degree

>>	Anonymous Sat Jan 20 13:13:26 2018 No.9451032 >>9450832 Im struggling in advanced calc, will I struggle in abstract algebra too?

>>	Anonymous Sat Jan 20 13:18:32 2018 No.9451043 >>9451014 >he doesn't know most engineers don't do engineering. I work at a fortune 50 company, my job title is engineer, but all i do is manage projects and move money around.

>>	Anonymous Sat Jan 20 13:24:02 2018 No.9451051 >professor wants to know our long-term career goals Is it okay if I just say I want to be a scientist?

Anonymous Sat Jan 20 13:29:44 2018 No.9451062
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>>9451026
Here were the positions. I don't know if I could get the job yet since I'm in 2nd year as an undegrad. I'll probably continue doing part-time work in the summer at my brother's place though doing basic network engineering work.

Anonymous Sat Jan 20 13:32:18 2018 No.9451069

>>9451002
Integrals are not antiderivatives. It's just a shitty notation, confusing people.
They are not entirely unrelated though since [math] \int_a^b f(x) dx = F(b) - F(a) [/math], if [math] F'=f [/math] in some region containing [math] [a,b] [/math] .

>>	Anonymous Sat Jan 20 13:33:21 2018 No.9451072 >>9451032 What is "advanced calculus"?

>>	Anonymous Sat Jan 20 13:35:18 2018 No.9451074 >>9451072 it's the high school level calculus class for the "advanced" kids.

>>	Anonymous Sat Jan 20 13:36:14 2018 No.9451078 >>9451072 At my uni "advanced calc" was real analysis. Not sure if this is true everywhere. Basically calculus but the emphasis is on proofs instead of computation.

>>	Anonymous Sat Jan 20 13:38:15 2018 No.9451082 >>9451078 advanced calc was a 3rd year course that covered stochastic calculus and calculus of variations. you could pick between that class and PDE's

Anonymous Sat Jan 20 13:47:19 2018 No.9451094
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Alright, so I understand what is happening here but I can't for the life of me figure out how I reach n(n+1)/2 . We basically create the sum of n - 1 until we reach 1, but how do I reach that formula where I can just insert n? I can't wrap my head around thinking in that manner if you know what I mean.

>>	Anonymous Sat Jan 20 13:49:25 2018 No.9451097 >>9451082 Oh that sounds interesting. My uni has a calculus of variations class on the catalog but it always gets cancelled due to low enrollment

>>	Anonymous Sat Jan 20 13:52:49 2018 No.9451105 >>9451094 [math] \sum_{k=0}^{n-1} (n-k) = \sum_{k=1}^n k [/math] Literally reverse the order of the sum and you get Gauss' formula.

>>	Anonymous Sat Jan 20 13:57:11 2018 No.9451111 >>9451105 Oh yea, I suppose that's true. I'm not a math student or anything, am I supposed to just remember that or what?

Anonymous Sat Jan 20 13:59:04 2018 No.9451114

So I have to solve this equation:
[eqn]u_{yy} - \frac{1}{(2x+1)^2}u_{xx} - \frac{2}{(2x+1)^3}u_{x} = 0[/eqn]
They ask me to solve it by putting it in its canonical form, which I manage to do no problem. But then how the fuck am I supposed to solve this bullshit?

[eqn]v_{\xi \eta} + \frac{1}{(2x+1)^2}v_{\xi} - \frac{1}{(2x+1)^2}v_{\eta}=0[/eqn]
where
[eqn]\xi (x,y) = y-x^2-x,\thinspace \eta(x,y)=y+x^2+x[/eqn]

How the fuck do I get [math]v[/math] from there? I'm pretty sure it's not wrong because several people have got to that equation and asked me how to do it, and I just don't know.

Anonymous Sat Jan 20 14:00:15 2018 No.9451116

>>9451111
>am I supposed to just remember that or what?

Well, Gauss' formula is pretty beautiful so you can memorize it just by instinct. I never actually sat down to memorize it, it just naturally digs itself into your brain because of how useful it is.

But if you are that lazy then simply remember that you can deduce Gauss's formula, and the formulas for [math] \sum k^a [/math] in general via summation by parts starting from the obvious fact that [math] \sum_{k=1}^n 1 = n [/math].

>>	Anonymous Sat Jan 20 14:01:34 2018 No.9451118 >>9451051 It's okay to not know and admit to it. Just bee urself, honestly.

>>	Anonymous Sat Jan 20 14:02:40 2018 No.9451119 >>9451082 I'm pretty jelly right now, my shitty uni doesn't have nice things like those. At least there's always the library, though.

>>	Anonymous Sat Jan 20 14:15:54 2018 No.9451137 File: 157 KB, 300x395, bookcover_n.png [View same] [iqdb] [saucenao] [google] name a more pretentious calc book. I'll wait

>>	Anonymous Sat Jan 20 14:20:45 2018 No.9451146 >>9451062 When youve taken ode, you could take any of those for sure. Could probably do most of them right now

>>	Anonymous Sat Jan 20 14:22:06 2018 No.9451149 >>9451072 Real analysis

>>	Anonymous Sat Jan 20 14:36:57 2018 No.9451166 what are some real life applications of calculus?

>>	Anonymous Sat Jan 20 14:37:11 2018 No.9451168 >>9451118 We're in a junior level class and most people are going to say they want to be a doctor. I know I want to do research/teach, what kind? I have no idea tbqh.

Anonymous Sat Jan 20 14:44:20 2018 No.9451177

>>9451166
Economics.

See, in our modern world there are too many pathways to success, but the wealth that we currently have and can produce is finite. It can only be split so thinly. So we have to face a reality: Either we all share it equally and basically, everyone is poor, or we create some kind of division between the rich and the poor so that the poor get scraps, and the rich get a lot. And here is where calculus comes in.

Can you pass the calculus sequence? Congratulations! Pick your job as an economist, engineer, physicist, computer scientist, etc. And then come to one of the thousands of corporations ready to pay you top dollar so that you can enjoy a great life.

You can't pass it? Congratulations! Head on over to the liberal arts to get ready for a life as a Starbucks barista making minimum wage. Thanks for playing!

Calculus is literally holding our economy together. It is the buffer. The limiting factor. It makes it so only a select group can become rich and powerful. And no one can argue with it because math is objective. You can't really go out crying that calculus is discriminatory unless you want to openly admit to being an absolute retard. And no one's pride is so low that they would publicly admit they are dumb. So society keeps working as intended. Thanks, Newton!

>>	Anonymous Sat Jan 20 14:45:44 2018 No.9451181 >>9451177 Could you please be more specific? Like state prominent examples like the Black-Scholes Equation

>>	Anonymous Sat Jan 20 14:47:13 2018 No.9451183 >>9451181 You didn't actually read my post, did you?

>>	Anonymous Sat Jan 20 14:49:26 2018 No.9451186 >>9450975 By conditions on x you get that [math]x(4-x)>0[/math] and can multiply both sides without worries, so [math]4\geq 4x-x^2\to x^2-4x+4=(x-2)^2\geq 0[/math]. Squares of reals are trivially non-negative.

>>	Anonymous Sat Jan 20 14:49:28 2018 No.9451187 >>9450832 tie in pic looks ridiculous

>>	Anonymous Sat Jan 20 14:52:36 2018 No.9451194 >>9451183 I did and I see how the gradient of the supply and demand slopes are of great significance, however, I was wondering if you could state a few more examples that involve some sort of derivation or integration.

Anonymous Sat Jan 20 14:54:51 2018 No.9451200

>>9451177
Fuck off bootlicker

You cant even get basic math right but youre trying to answer a question on calculus.

Retard, the top 10% of people own over 50% of the wealth on tbe entire planet. If that 50% of wealth was redistributed equally, the vast majority of people would see INCREASE in wealth.

Calculus is not tbe limiting factor between the rich and poor. Put a day 1 calc I problem in front of Trump and see if he can solve it. Or Steve Jobs or Bezo or Koch or Mercer. None of those rich dumbasses know calculus.

>>9451166
Most engineering fields use it regularly. Building infrastructure, new technologies. Most physicists probably use it in their research. Biologists might use it to model bacteria growth or something. Economists, actuaries use it for optimizations. And more

Anonymous Sat Jan 20 14:56:39 2018 No.9451205

>>9450975
Let [math] x \in (0,4) [/math]. In this interval we have that [math] x(4-x) > 0 [/math] which means that we can manipulate inequalities without changing signs: So

[math] \frac{4}{x(4-x)} \geq 1 \iff 4 \geq x(4-x) \iff x^2 -4x + 4 \geq 0 \iff (x-2)^2 \geq 0 [/math] which is trivially true.

Anonymous Sat Jan 20 15:01:10 2018 No.9451213

>>9451200
>the vast majority of people would see INCREASE in wealth

Yeah but that "increase" would still put them below the poverty line. Do you know how many people there are alive today? Go on, pile up all the wealth and then give everyone an equal amount of it. You will be lucky to end up with 5$ each. Good luck with that mate.

>Put a day 1 calc I problem in front of Trump and see if he can solve it. Or Steve Jobs or Bezo or Koch or Mercer. None of those rich dumbasses know calculus.

That is not what I meant, which shows in what category you belong to lol. I said that Calculus is just the buffer. If you pass it, you are good. You don't need to keep knowing calculus. You know what major Trump studied, which means he had to pass calculus and he did. So he was allowed into the big boys club. After that it was his other actions that decided how rich he got, but getting into the big boys club guaranteed he would at least be middle class. The same goes for everyone else you listed.

If Steve Jobs had fucking failed calculus do you think he would have had the opportunity to start a corporation? If he could not pass calculus, his IQ would be approximately 80. He would be lucky to be able to tie his shoes.

>>	Anonymous Sat Jan 20 15:01:51 2018 No.9451215 >>9451032 Well, if it's real analysis, then maybe you can do ok in Algebra. Algebra has a more "natural" way of thinking.

>>	Anonymous Sat Jan 20 15:10:33 2018 No.9451230 >>9451213 >iq memer >bootlicker >"corporations are great!" >im wrong? move those goalposts! >calls calculus a buffer but cant do an optimization problem >thinks wealth necessitates intelligence is race "r e a l"?

>>	Anonymous Sat Jan 20 15:11:24 2018 No.9451233 >>9451137 how can a calculus book be pretentious?

>>	Anonymous Sat Jan 20 15:11:50 2018 No.9451234 >>9451230 >"corporations are great!" Never said that. But corporations are great at making big money. If you deny that, you are retarded. >thinks wealth necessitates intelligence Have you ever observed how stupid people use their money?

Anonymous Sat Jan 20 15:13:03 2018 No.9451236

>Write down the balanced reaction equation for the reaction of chromium oxides with nitric acid.
>What kind of reaction occurs?

>write down the balanced reaction equation.
ok, I can do that.
>for the reaction of chromium oxide with nitric acid.
So, do they want me to guess the product?
>What kind of reaction occurs?
Yeah, a reaction.
So, is there a special kind of place I need to look up how to monkey see and monkey do?

>>	Anonymous Sat Jan 20 15:55:55 2018 No.9451289 Why the FUCK is n^3 + 1 NEVER prime (except when n=1) I can trivially prove it for odd n but can't prove it for even n

>>	Anonymous Sat Jan 20 15:57:14 2018 No.9451292 File: 19 KB, 417x175, Untitled.png [View same] [iqdb] [saucenao] [google] help

>>	Anonymous Sat Jan 20 15:59:24 2018 No.9451294 I keep breaking pens. How do you deal with the frustration of not understanding?

>>	Anonymous Sat Jan 20 16:04:06 2018 No.9451301 File: 313 KB, 1398x1985, 81SXgQ+oFyL.jpg [View same] [iqdb] [saucenao] [google] >>9451137 >name a more pretentious calc book.

>>	Anonymous Sat Jan 20 16:07:05 2018 No.9451304 >>9451292 The statements contradict each other what the fuck am I supposed to do

>>	Anonymous Sat Jan 20 16:08:23 2018 No.9451306 >>9451289 >Why the FUCK is n^3 + 1 NEVER prime (except when n=1) >I can trivially prove it for odd n but can't prove it for even n Plug (2n)^3+1 into Wolfram, and it'll show you that (2n)^3+1=(2n+1)(4n^2-2n+1)

>>	Anonymous Sat Jan 20 16:09:32 2018 No.9451307 >>9451289 >>9451306 Also it's just the sum of cubes formula http://www.purplemath.com/modules/specfact2.htm

>>	Anonymous Sat Jan 20 16:09:50 2018 No.9451308 >>9451306 Oh duh I was just staring at that. Thanks my negroid

>>	Anonymous Sat Jan 20 16:30:29 2018 No.9451335 Is this true or not? [math] \sum_{k=1}^n ( \lg (n) - \lg (k)) = O(n) [/math]

>>	Anonymous Sat Jan 20 16:33:41 2018 No.9451341 >>9451335 >Is this true or not? Why might it be true?

Anonymous Sat Jan 20 17:12:44 2018 No.9451410

>>9450832
Say you have an infinite lattice of points and paths that connect them such that at any point there are 4 paths leading away from it. Further suppose that you pick a path at random, then what is the probability that you will eventually reach a point one "step" away?

The way I worked this is:
Probability of getting to the point after one step: [math] \frac { 1 } { 4 } [/math]
After three steps: [math] \frac { 1 } { 4^3 } [/math]
After 2n+1 steps: [math] \frac { 1 } { 4^{(2n+1)} } [/math]

So we end up with the series:
[eqn] \frac { 1 } { 4 } \sum _{ n=0 } ^{ \infty } \frac { 1 } { 4 ^{2n } } [/eqn]So we get a probability of reaching the neighboring point of: [eqn] \mathbb { P } = \frac { 4 } { 15 } [/eqn]

Does that seem right to everyone else?

>>	Anonymous Sat Jan 20 17:19:22 2018 No.9451420 >>9451410 >Probability of getting to the point after one step: 1/4 Shouldn't this probability be 1?

>>	Anonymous Sat Jan 20 17:20:32 2018 No.9451422 Why is some snow easier to pack into snowballs than other?

>>	Anonymous Sat Jan 20 17:23:48 2018 No.9451426 >>9451420 Why would it be? By hypothesis you have a 1/4 chance of picking the path that takes you the end point on your first go.

Anonymous Sat Jan 20 17:27:59 2018 No.9451435

>>9451072
>The term Advanced Calculus has come to mean different things over the course of the past century. During the first half of the 20th century, Advanced Calculus courses consisted of what's now commonly found in Multivariable and Vector Calculus possibly with some Differential Equations topics thrown in. Lately, it has been fashionable to call very watered down "Real Analysis" courses Advanced Calculus even though it's not [math]advanced[/math] nor [math]calculus[/math] and goes no deeper into analysis than a good rigorous calculus book does. Here Advanced Calculus means what the name implies, advanced topics in calculus (and tools from analysis) typically not found in the usual calculus sequence but still very useful for solving difficult problems in science, engineering, and mathematics.
>http://4chan-science.wikia.com/wiki/Mathematics#Advanced_Calculus

>>	Anonymous Sat Jan 20 17:29:08 2018 No.9451436 >>9451426 >Why would it be? After one step you have reached a point one step away.

Anonymous Sat Jan 20 17:33:10 2018 No.9451445

>>9451137
>Early Transcendentals
All that mean is they cover the Transcendental functions early (trigonometric, exponentials, logarithms) rather than wait until they get to power series and DEs to define them by calculus.

Also Rogawski is terrible for self study.

>>	Anonymous Sat Jan 20 17:35:38 2018 No.9451452 >>9451436 No, you have a 1/4 chance of reaching the end in one step.

Anonymous Sat Jan 20 17:43:01 2018 No.9451469

>>9451452
>No, you have a 1/4 chance of reaching the end in one step.
So when you said
> Further suppose that you pick a path at random, then what is the probability that you will eventually reach a point one "step" away?
You had a specific point in mind of the four that are one step away? In that case the probability of reaching it after 3 steps is certainly higher than 1/4^3, I count at least 7 walks

>>	Anonymous Sat Jan 20 17:48:11 2018 No.9451477 >>9451469 >You had a specific point in mind of the four that are one step away? Yep. > I count at least 7 walks How?

>>	Anonymous Sat Jan 20 17:49:38 2018 No.9451479 >>9451477 >How? If the end point is the one above your starting point, then you can do (L= left, R= right, U=up, D=down): LUR, RUL, DUU, UUD, UDU, LRU, RLU

>>	Anonymous Sat Jan 20 17:51:08 2018 No.9451484 >>9451479 Yeah, just realised that. Thanks anon.

>>	Anonymous Sat Jan 20 18:04:02 2018 No.9451509 >>9450832 What is the product of every number greater than 0? I think it's 1, but not sure

>>	Anonymous Sat Jan 20 18:05:50 2018 No.9451511 >>9451509 >I think it's 1 That's correct.

>>	Anonymous Sat Jan 20 18:10:05 2018 No.9451517 >>9451511 Eh, sure it isn't undefined? Depending on how you pair the infinitesimals and -->infinites you should be able to make it sum whatever as you take the limit.

>>	Anonymous Sat Jan 20 18:12:31 2018 No.9451524 >>9451517 >Eh, sure it isn't undefined? \prod_{x>0} x = 1(\prod_{x>1} x)(\prod_{x<1} x) = (\prod_{x>1} x)(\prod_{x>1} 1/x) = \prod_{x>1} 1 = 1

>>	Anonymous Sat Jan 20 18:17:41 2018 No.9451532 >>9451524 Ah right yeah no bypassing numbers, no funky summations. You're right.

>>	Anonymous Sat Jan 20 18:20:23 2018 No.9451535 Why the shitnigger does 2^0 + 2^1 + ... + 2^n = 2^{n+1} - 1 @perfect binary trees

>>	Anonymous Sat Jan 20 18:21:44 2018 No.9451537 >>9451535 >Why the shitnigger does >2^0 + 2^1 + ... + 2^n = 2^{n+1} - 1 https://en.wikipedia.org/wiki/Geometric_series

>>	Anonymous Sat Jan 20 18:25:52 2018 No.9451543 >>9451537 o fuck

>>	Anonymous Sat Jan 20 18:30:57 2018 No.9451550 How important is the right latin ending of a word in an anatomical context really?

Anonymous Sat Jan 20 18:59:53 2018 No.9451596

>>9451292

Assuming knights are honest and knaves lie:
There must be some knights, and it can't include U. If he was a knight, he's lying. If he's not a knight, there must be another to make sure he's lying.

Of X, Y, and Z: mutually exclusive. We have to look at V and W.
If Z is a knight, W is a knight. Z is now lying, so he's a knave.
If Y is a knight, W is a knight. Everyone else is a knave, so this works.

For the sake of completion, X is trivially a knave just by looking at Y and Z.

>>	Anonymous Sat Jan 20 19:06:24 2018 No.9451609 >>9451535 Look at it in binary 1 + 10 + 100 + ...

>>	Anonymous Sat Jan 20 19:08:39 2018 No.9451615 >>9451596 >Assuming knights are honest and knaves lie: So THAT'S the missing knowledge he couldn't tell us >>9451609 Good observation

>>	Anonymous Sat Jan 20 20:13:49 2018 No.9451697 how do babies make any evolutionary sense? they are completly dependent untill about age 7 or so, so for those 7 years you have to waste time and energy to this thing that cannot fend for itself

>>	Anonymous Sat Jan 20 20:15:07 2018 No.9451700 protip to help you remember pi you can use the apporimation 314,159/100,000

Anonymous Sat Jan 20 20:16:05 2018 No.9451703

>>9451697
>how do babies make any evolutionary sense? they are completly dependent untill about age 7 or so, so for those 7 years you have to waste time and energy to this thing that cannot fend for itself
https://en.wikipedia.org/wiki/R/K_selection_theory

>>	Anonymous Sat Jan 20 20:18:56 2018 No.9451707 >>9451700 i have the first 60 digits of pi tattooed on my dick so if i ever need it on a test, i just get hard on the spot. fuck memorization

>>	Anonymous Sun Jan 21 01:10:25 2018 No.9452355 File: 31 KB, 192x452, wow.jpg [View same] [iqdb] [saucenao] [google] If the uniform metric C(X,Y) on metric spaces X and Y is complete, does that entail that Y is complete?

Anonymous Sun Jan 21 01:13:13 2018 No.9452360
File: 239 KB, 640x926, 5854669a9d3d1aa75a6509778e8a54f8.jpg [View same] [iqdb] [saucenao] [google]

Can anyone give me a straight answer on what specific algorithm's are used to generate/compute new prime numbers are? I really would like to know because I think I may have stumbled onto a relatively trivial way of computing increasingly large prime numbers but I feel like it may already be utilized and I honestly don't even fully understand why it works.

Pic unrelated btw

Anonymous Sun Jan 21 01:40:14 2018 No.9452381

Anyone have any good recs doe basic logic? I remember taking an intro to logic class back in college. I don't remember a lot, just basically that it was 'math with words' I remember one of the rules was a motis ponens(sp?) and it basically let you set up logic problems and use those rules to confirm or deny. I'm just looking for a decent comprehensive book that will cover the basics.

>>	Anonymous Sun Jan 21 01:44:56 2018 No.9452385 File: 17 KB, 316x239, 1448044638406.jpg [View same] [iqdb] [saucenao] [google] >>9452360 i saw this exact post work for word on r badmath you fucking c*ck. go back to r#ddit

>>	Anonymous Sun Jan 21 01:57:49 2018 No.9452395 >>9450972 non-inertial reference frames are garbage; it's hard to predict anything with them. dp/dt is the definition of force, so it always applies, but it will be meaningless in a non-inertial frame.

>>	Anonymous Sun Jan 21 02:03:58 2018 No.9452400 >>9452385 Could you please attempt to offer an intelligent answer to my question instead of acting like a cunt to stroke your e-peen? It's a legitimate question that I've been going in circles trying to find a straightforward answer to.

Anonymous Sun Jan 21 02:28:22 2018 No.9452422

>>9451292
-U cannot be a knight
-X contradicts Y and Z, thus he cannot be a knight
-Of the remaining possible knights, V can only be in agreement with W. This falls short of 3, so V cannot be a knight.
-if Z is correct, then W is also correct, leading to a contradiction. Z is not a knight.
-at this point we've eliminated 4 of the 6, so W is correct. If Y is wrong, that would make Z correct, leading to a contradiction. Thus, W and Y are knights.

Anonymous Sun Jan 21 02:31:07 2018 No.9452425

>>9452355
Let [math] y_n [/math] be a Cauchy sequence of [math] Y [/math] .
Consider the sequence [math] f_n [/math] of [math] C(X,Y) [/math] where [math] f(x)=y_n [/math] for all [math] x \in X [/math] (constant functions).
[math] d(f_n,f_m)= \sup_{x \in X} d(f_n(x),f_m(x)) = \sup_{x \in X} d(y_n,y_m) = d(y_n,y_m) \to 0 [/math] (d denotes three different metrics here)
Therefore [math] f_n [/math] is a Cauchy sequence of [math] C(X,Y) [/math], and since [math] C(X,Y) [/math] is complete it converges to some [math] f \in C(X,Y) [/math] .
[math] f [/math] has to be a constant function as well since [math] d(f(x_1),f(x_2)) \leq d(f(x_1),y_n) + d(f(x_2),y_n) \leq d(f,f_n) + d(f,f_n) \to 0 [/math] which implies that [math] d(f(x_1),f(x_2))=0 [/math] , which means that [math] f(x_1)=f(x_2) [/math] for all [math] x_1,x_2 \in X [/math] .
Denote with [math] y [/math] the constant value of [math] f(x) [/math] .
[math] d(y_n,y) = d(f_n(x),f(x)) = \sup_{x \in X} d(f_n(x),f(x)) \to 0 [/math].
So, [math] y_n \to y [/math] .

>>	Anonymous Sun Jan 21 02:35:34 2018 No.9452429 What are some of the best resources for Chem E Transport? Also, is it actually important or just a way for Chem Es to stroke their egos? Either way, resources please, my prof isn't doing it for me and I'd like to learn.

Anonymous Sun Jan 21 04:35:40 2018 No.9452530

>>9450896
>short
https://www.amazon.com/Calculus-Made-Easy-Silvanus-Thompson/dp/0312185480/
https://www.amazon.com/Manga-Guide-Calculus-Hiroyuki-Kojima/dp/1593271948/

>long
https://www.amazon.com/Calculus-Lifesaver-Tools-Princeton-Guides/dp/0691130884/
https://www.amazon.com/Calculus-Intuitive-Physical-Approach-Mathematics/dp/0486404536/

>>	Anonymous Sun Jan 21 04:37:19 2018 No.9452533 >>9452381 http://4chan-science.wikia.com/wiki/Mathematics#Proofs_and_Mathematical_Reasoning

>>	Anonymous Sun Jan 21 04:38:26 2018 No.9452534 >>9452429 http://4chan-science.wikia.com/wiki/Chemical_Engineering#Transport_Phenomena

>>	Anonymous Sun Jan 21 06:46:14 2018 No.9452607 >>9451422 It's easiest when it's near 0C. Pressuring the snow melts a fraction of it, and the water acts as glue. See P* at https://en.wikipedia.org/wiki/Types_of_snow#On_the_ground

>>	Anonymous Sun Jan 21 09:30:04 2018 No.9452753 Ok guys, Im a MSc biochemistry student about to do a lab internship. How can I be creative enough to plan and conduct my own research about a certain matter? I really want to do my best and try to impress my supervisors to get a job here.

>>	Anonymous Sun Jan 21 09:50:41 2018 No.9452786 >>9452429 Not a chem eng major but some who are have said its their first real class so Id say its important

Anonymous Sun Jan 21 09:54:22 2018 No.9452789

>>9452753
What I did for my project (not in chem tho) was search google, arxiv and any other relevant sites for the latest research in my field and found a topic that looks interesting/i had the resources for doing.

My professors are utterly useless, if yours arent, you should talk to them

>>	Anonymous Sun Jan 21 10:04:03 2018 No.9452807 >>9452753 >>9452789 yeah, can try to impress them with knowledge on recent research, but in the end, they know it better, and you are supposed to do what they ask or tell you to do

Anonymous Sun Jan 21 10:17:35 2018 No.9452826

>>9450832
I've really been getting into YouTube videos about quantum theory and I feel like its hard to conceptualise things like wave functions and the higgs field from just a video and I'd like to know what the best resources are for first reads on quantum theory and relativity. No resources on science from /lit/ or /sci/s sticky so sorry if this is a common question

Anonymous Sun Jan 21 10:22:22 2018 No.9452828

>>9452789
>>9452807
oh i dont think ive expressed myself correctly. I have a certain subject I have to hold to of course. The only thing is my supervisor said you can try and do your own research about this matter (i still have to get approval). So what I'm asking is how do researchers come up with shit they want to study on a certain subject. I know you have to read a lot of papers but still the creativity they have seem insane to me.

Anonymous Sun Jan 21 10:50:22 2018 No.9452850

>>9452828
I still think following up on recent research applies. Ex I did a project within plasma physics so I searched a plasma journal and found that researchers are placing plasma generators on 18wheeler trucks to reduce drag. So I wrote a simulation of that and tried to do a miniature experimental version of it in lab.

Um. Other things to think about. What is the area that your lab is in? Consider problems in the field. Consider anything that could be improved. Any gaps that could be filled.

If that doesnt do it for you, you could replicate a previous experiment done by the lab to verify it.

Is that the info youre looking for?

>>	Anonymous Sun Jan 21 10:56:34 2018 No.9452857 Resources on writing scientific research papers?

>>	Anonymous Sun Jan 21 10:59:49 2018 No.9452861 >>9452850 alright thanks man I guess it also depends on the experience. Practice makes perfect after .

Anonymous Sun Jan 21 11:24:18 2018 No.9452883
File: 109 KB, 1280x720, glacier.jpg [View same] [iqdb] [saucenao] [google]

How much pressure do you need to form glacial ice out of firn? All the sources I can find always simply talk about a large amount, but how much pressure are we talking about here?

>>	Anonymous Sun Jan 21 11:28:57 2018 No.9452888 >>9452530 >https://www.amazon.com/Manga-Guide-Calculus-Hiroyuki-Kojima/dp/1593271948/ Holy shit that's like the best manga series ever

Anonymous Sun Jan 21 11:44:52 2018 No.9452914

>>9452857
https://www.google.com/search?q=how+to+write+a+research+paper

>0. Abstract
intro: Wouldn't it be awesome and useful if we could do X? No one has ever done X before.
body: We did X, here's what it looks like/here are the results.
conclusion: X is awesome, we did it first.

>1. Introduction
Background about the subject, brief elaboration on what's already known about it and what still has to be done, before going on to briefly discuss what you did, and if necessary what methods you use and why in very general terms.

>2. Materials and methods
Technical description of what you did. Not complete protocols, but in principle people should be able to reproduce your experiment from what's in this section. That said, this section is often not broad enough for that. A lot of journals do offer supplementary methods online, though.

>3. Results
What you saw. A very objective and neutral description of your results. "We observe x with a p-value of y." No interpretations yet.

>4. Discussion and conclusion
How should we interpret these results? What might have influenced them? What are downsides of our study? Also you can cite some papers that support or contradict your results and argue why your results are good.

>5. References
obv

>>	Anonymous Sun Jan 21 12:00:40 2018 No.9452937 >>9452914 thanks mate, very helpful

>>	Anonymous Sun Jan 21 12:11:52 2018 No.9452958 >>9452937 not him but you should also note that there are different uses of tenses in different parts of the paper. Like past tense in introduction when you're stating facts. I don't know all of them by memory but a simple google search should help you

>>	Anonymous Sun Jan 21 12:15:44 2018 No.9452965 Why are people writing papers on stuff they've just red?

>>	Anonymous Sun Jan 21 12:30:38 2018 No.9452985 >>9452937 it's original /sci/ copy pasta anyway >>9452958 care to explain?

>>	Anonymous Sun Jan 21 12:34:28 2018 No.9452989 >>9450832 dumb question: If we put n=1 why >nxn >2n gives different results? i feel very stupid for not understanding it

Anonymous Sun Jan 21 13:08:15 2018 No.9453039

so, I want to learn me a haskell. it'll be my first language if you don't count Matlab from school.

is there any website, book or series of youtube videos that treats me like a retard and holds my hand through picking a text editor, installing the language, compiling etc? I really don't know where to even begin

Anonymous Sun Jan 21 13:18:49 2018 No.9453049

I was reading about nuclear arms and dooms day machines, and the Teller-Ulam design came up (the use of radiation pressure to cause fusion - hydrogen bomb).

https://en.wikipedia.org/wiki/Radiation_implosion
and
https://en.wikipedia.org/wiki/Radiation_pressure

Is it possible "feel" radiation pressure similar to air pressure (also is it possible to feel it dying)?

>>	Anonymous Sun Jan 21 13:19:54 2018 No.9453051 >>9453039 People on the daily programming thread on /g/ might help you

>>	Anonymous Sun Jan 21 13:30:15 2018 No.9453067 >>9453051 ok thanks

Anonymous Sun Jan 21 14:37:40 2018 No.9453183

>>9452826
>quantum theory
I don't know about this stuff, but I've always heard physicists (both friends and in /sci/) give the same references: Sakurai, Cohen-Tanoudji and sometimes Griffiths and Landau, start with the first two, the last two I've heard are not as recommended.

>>	Anonymous Sun Jan 21 14:50:55 2018 No.9453207 can someone give me some intuition behind filters and ultra filters on a set?

>>	Anonymous Sun Jan 21 14:53:41 2018 No.9453210 >>9452989 >If we put n=1 why >>nxn >>2n >gives different results? i feel very stupid for not understanding it Because 2n = n + n, not nxn (which would be n^2)

Anonymous Sun Jan 21 15:01:22 2018 No.9453225

This may be brainlet as fuck, but... is there an intuitive way to understand equivalence relations and partitions?

I know their definition, and I have no problem with proving that a relation is a relation of equivalence, but my professors often use and talk about them as if they could "visualize" something. Any thoughts?

Anonymous Sun Jan 21 15:08:47 2018 No.9453242

>>9453225
>I know their definition, and I have no problem with proving that a relation is a relation of equivalence, but my professors often use and talk about them as if they could "visualize" something. Any thoughts?
The extent of "visualizing" depends on the partition but for example the equivalence relation on R^2 given by (x,y)~(a,b) iff y=b gives you equivalence classes that are horizontal lines

>>	Anonymous Sun Jan 21 15:52:48 2018 No.9453332 >>9452425 Thanks a bunch, it was not entirely clear to me that this statement was true

>>	Anonymous Sun Jan 21 15:55:26 2018 No.9453339 File: 35 KB, 600x645, 824.jpg [View same] [iqdb] [saucenao] [google] How to pronounce [math] \nabla f [/math] ?

>>	Anonymous Sun Jan 21 15:59:04 2018 No.9453343 >>9453339 grad f

>>	Anonymous Sun Jan 21 16:00:48 2018 No.9453346 >>9453339 nabla f

>>	Anonymous Sun Jan 21 16:05:34 2018 No.9453353 >>9453339 "gradient of f"

Anonymous Sun Jan 21 16:15:14 2018 No.9453364

>>9453353
"Gradient" can be a bit of a tongue twister at times. I'd have to repeat "gradient of f" more than 8 times explaining the proof of a simple formula. Add exam stress into the equation and you get a barely intelligible answer.
>>9453346
Sounds more like it. Thanks.

>>	Anonymous Sun Jan 21 16:15:16 2018 No.9453365 File: 63 KB, 400x600, 1498335356683.jpg [View same] [iqdb] [saucenao] [google] Hard mode: How to pronounce: [math]M_{\mathscr{T}\leftarrow\mathscr{B}}(T)[/math]

Anonymous Sun Jan 21 16:18:53 2018 No.9453376
File: 1.98 MB, 400x250, 1516459401839.gif [View same] [iqdb] [saucenao] [google]

>>9453183
>samurai 70$ on amazon
>no results for Cohen on amazon bookstore

This isn't going to be easy is it... Any thoughts or
recommendations for entry level relativity? I found some deep lecture notes for physics in /sci/s wiki, which BTW should totally be linked in the sticky but oh well.

Anonymous Sun Jan 21 16:19:15 2018 No.9453377

>>9450832
I've been thinking and maybe we should collect data from /sci to get some age, or education distributions and the data would be collected with polls, and I was wondering what kind of data we would like to see, so I can know what to ask in the polls?

>>	Anonymous Sun Jan 21 16:20:05 2018 No.9453379 File: 961 KB, 672x877, Screenshot_2018-01-21_17-49-49.png [View same] [iqdb] [saucenao] [google] >>9453376 got this on libgen

>>	Anonymous Sun Jan 21 16:24:43 2018 No.9453392 >>9453376 You can always pirate that stuff, or buy them second hand. A friend of mine got Cohen for 25€ that way.

>>	Anonymous Sun Jan 21 16:29:00 2018 No.9453401 >>9453339 "dell f"

>>	Anonymous Sun Jan 21 16:46:03 2018 No.9453435 >>9452534 >>9452786 Thanks, bros

>>	Anonymous Sun Jan 21 17:08:18 2018 No.9453470 >>9453225 A partition is simply a way to group the elements of a set into disjoint subsets, like putting books on shelves or files in separate folders. An equivalence class would simply be a folder.

Anonymous Sun Jan 21 17:09:47 2018 No.9453473

Let [math]f:X\to Y[/math] be a function and define [math]g:Y\to X[/math] such that [math]g\circ f = I_{x}[/math]. Prove [math]f[/math] is injective.

Is this a proper proof?
If [math]f[/math] is injective, let [math]x_{1},x_{2}\in X [/math] and [math]f(x_{1})=f(x_{2})[/math]. The composition of [math]f[/math] and [math]g[/math] is well defined, so [math]g(f(x_{1})) = g(f(x_{2})) \iff (g\circ f)(x_{1})=(g\circ f)(x_{2}) \iff I_{x}(x_{1}) = I_{x}(x_{2}) \iff x_{1} = x_{2}[/math]

Anonymous Sun Jan 21 17:28:36 2018 No.9453505

>>9453473
Almost. You can't do a proof by assuming the thing you're trying to prove is true, as in "If [math]f[/math] is injective ... ." Cut that part out and use the fact you've proven [math]\left( f(x_1) = f(x_2) \iff x_1 = x_2 \right)[/math] imply [math]f[/math] is injective by definition.

>>	Anonymous Sun Jan 21 17:34:57 2018 No.9453513 >>9453505 Alright, thanks.

>>	Anonymous Sun Jan 21 17:50:21 2018 No.9453537 File: 20 KB, 643x100, 4733b768d4cf71d8a72495866bb287c3.png [View same] [iqdb] [saucenao] [google] How do I define the basis here? Could I just assign an arbitrary variable to be aT^2 + aT + b, and just assume that to be the basis, and then dim V = 1?

Anonymous Sun Jan 21 17:59:37 2018 No.9453554

>>9453537
I don't feel like this question is being properly asked, but without further context, the only interpretation I can give is:

[math] B = \{ T^2 + T, 1 \} [/math] which is a basis as every element of V is a linear combination of these elements and it can trivially be shown that no single element can completely span the set.

That said, if what I said just made sense to you and you see this is the correct solution then I have to tell you this is the dumbest exercise that they could propose. Change textbooks immediately.

>>	Anonymous Sun Jan 21 18:09:27 2018 No.9453567 Does anybody know a rigorous mathematical definition of the Degrees of Freedom of a Random Variable? All I have found after googling is unrigorous engineer-tier bullshit full of meaningless words.

>>	Anonymous Sun Jan 21 18:10:34 2018 No.9453571 >>9453339 "Dee ef" And you should write it [math] Df [/math] .

>>	Anonymous Sun Jan 21 18:15:02 2018 No.9453579 >>9453554 It does make sense thank you. And I wish I could, but we are using a professor's textbook and it's absolute garbage. Learning from the Howard Anton text instead.

>>	Anonymous Sun Jan 21 18:17:41 2018 No.9453585 File: 42 KB, 931x194, Capture.png [View same] [iqdb] [saucenao] [google] i cant figure out the second part.

>>	Anonymous Sun Jan 21 18:42:41 2018 No.9453627 File: 7 KB, 504x105, .png [View same] [iqdb] [saucenao] [google] Can someone tell me what the fuck is happening here? These are the solutions to a problem my teacher gave and there is no explanation whatsoever about what is happening here.

>>	Anonymous Sun Jan 21 18:47:08 2018 No.9453634 >>9453585 So, lets call v=(0,-v), if he is swimming across then u=(+-u_1,v) and u_i=sqrt(u^2-v^2) so t_2=2L/u_i=2L/u/sqrt(1-(v/u)^2) t_1=L/(u-v)+L/(u+v)=2Lu/(u^2-v^2)=2L/u/(1-(v/u)^2) t_2/t_1=sqrt{1-(v/u)^2}

>>	Anonymous Sun Jan 21 18:47:50 2018 No.9453635 >>9453627 Hint: Think In all seriousness, it is clear that what they did was add every other column to the first column. This operation preserves determinant (Proof: Think).

>>	Anonymous Sun Jan 21 18:50:33 2018 No.9453638 >>9453585 second part: [eqn]u_x^2+u_y^2=u^2\\v_x^2+v_y^2=v^2\\ v_x=0\\ v_y=u_y[/eqn]

>>	Anonymous Sun Jan 21 18:54:33 2018 No.9453645 File: 268 KB, 2560x1440, Screenshot_20180122-005157.png [View same] [iqdb] [saucenao] [google] >>9453627 look at D7, its a property of the determinant. altough mine slightly difers from your

Anonymous Sun Jan 21 19:05:29 2018 No.9453657

>>9453635
>add every other column to the first column
>This operation preserves determinant
Thanks for the information. I had no clue and I don't think I'd find out by thinking about it myself. To be honest I am quite frustrated with all this right now, my professor knows his stuff but has absolutely no merit as a teacher. I am working through his book right now and it is taking all the joy out of math that I might have had otherwise, he is just incapable of explaining something in humanly understandable terms and uses horrible "examples" to illustrate his undecipherable ramblings. Not to mention his book is full of careless mistakes, because he clearly wrote it all without anybody actually looking over it. God I wish I could just work through something substantial right now, but the exam is in 2 weeks. It's probably just a bad combination of bad teacher and not very good student. Sorry for my rambling.

>>9453645
That's adding rows and not columns though. I did know that worked but that's not what is happening there. I suppose it works in the same way?
I don't know.

>>	Anonymous Sun Jan 21 19:06:13 2018 No.9453659 Show that if [math]X[/math] and [math]Y[/math] are sets, then [math]X\cross Y ~ Y \cross X [/math] Would this just be [math]f:Y\to X[/math] defined by [math]f^{-1}(y)=x[/math] , which is obviously a bijection?

Anonymous Sun Jan 21 19:16:16 2018 No.9453681

>>9453657
>I had no clue
Well, let me tell you it is a bad idea to be doing problems about determinants when you don't know the properties of determinants. And there are quite a few.

>I don't think I'd find out by thinking about it myself
It is a joke, but if you meditate over the geometric definition you might discover this property as it is necessary for it to have its geometric properties. And if your determinant was defined algebraically then you know that the determinant is the unique function with 3 certain properties, and from these 3 properties, the fact I mentioned can be deduced very easily.

>I am working through his book
Ah, so you are the guy I helped before with the [math] aT^2 + aT + b [/math] problem.

>>9453657
>That's adding rows and not columns though
That does not matter. Remember that the transpose operation also preserves determinant, so as far as the determinant is concerned, columns work just like rows.

Must suck having a shitty teacher. Linear Algebra was so fun, and it is really useful. Don't neglect this stuff. You see matrices everywhere. I am right now taking a break from studying number theory, where I saw how matrices were used to deduce the properties of Abelian characters, with the purpose of proving the main properties of Dirichlet characters, with the purpose of proving Dirichlet's theorem on primes in arithmetic progressions.

Linear Algebra is everything!

>>	Anonymous Sun Jan 21 19:21:43 2018 No.9453695 >>9453659 How do you know an bijection exists between X and Y?

Anonymous Sun Jan 21 19:24:27 2018 No.9453700

>>9453681
I don't think I was that guy, suppose there isn't only one professor doing a shoddy job so they can profit off of their students.
And thank you for all the help man, you're really a great guy. I wish I could properly deduce and understand all of it, but like I said, this book is just useless and I don't have the time to go work through something else so I am just learning how to solve the problems and hope I can pass the exam. I'm not a math student in the first place, so I need to study for other subjects as well.
Man I wish I was someone else right now.

Anonymous Sun Jan 21 19:36:37 2018 No.9453713
File: 133 KB, 750x1334, t9fidjskix901.jpg [View same] [iqdb] [saucenao] [google]

So differential k-forms are things you combine with k-dimensional surfaces on an n-dimensional ambient manifold with [math]\int[/math] to get a scalar (right?)

Is there anything else you can do with them?

>>	Anonymous Sun Jan 21 19:40:32 2018 No.9453717 File: 481 KB, 760x1344, 1512289760231.jpg [View same] [iqdb] [saucenao] [google] >>9453713

Anonymous Sun Jan 21 19:44:14 2018 No.9453723

>>9453700
>suppose there isn't only one professor doing a shoddy job so they can profit off of their students

That really sucks. None of my professors ever push their own books, which is interesting as they always recommend at least 5 different texts which means they have a lot of room to sneak their own.

>>9453700
>this book is just useless and I don't have the time to go work through something else so I am just learning how to solve the problems

More power to you but the problem with that is that problem solving is meant to be "in the moment". You are never supposed to "know" how a problem is solved, you are just supposed to be able to quickly recall the relevant facts to start hitting the problem with until a solution is found.

The best strategy is always to have the fundamentals memorized and well-practiced. I see very little value in doing problems without understanding the theory. There is never a guarantee that the exam problems will be of the same difficulty as the typical exercise found in textbooks.

Anonymous Sun Jan 21 20:28:01 2018 No.9453780

>>9453723
In principle I agree with you 100% but this is just my shitty reality.
I'm still a first semester, had litte math beforehand and I underestimated the workload. Now I really don't have a choice anymore, there is no way I can catch up that amount of stuff. Sadly I'm not really allowed to repeat a semester because I will lose my source of income. Hopefully I can pass the exam with the way I am studying and I will use the entire holidays to get on understanding everything properly and thoroughly so I won't have problems in the future.
I think university is different in the US actually? That the first semester or the first year is used to bring everyone on the same level or something, I think I read something about that but I'm not sure anymore. Here they just throw everyone into the cold water and the people who can't keep up fly out.

Anonymous Sun Jan 21 20:33:14 2018 No.9453788

>>9453657
Read Axler's Book (it won't help you with determinants though). You could pirate it (from bookfi for example), but that would be illegal, so don't do it :)

Check 3Blue1Brown's "Essence of Linear Algebra" playlist.
https://www.youtube.com/playlist?list=PLZHQObOWTQDPD3MizzM2xVFitgF8hE_ab

Also, for determinants, check these two lectures:
https://www.youtube.com/watch?v=23LLB9mNJvc
https://www.youtube.com/watch?v=srxexLishgY

>>	Anonymous Sun Jan 21 20:34:34 2018 No.9453791 >>9453657 >That's adding rows and not columns though. I did know that worked but that's not what is happening there. I suppose it works in the same way? I don't know. [math] \det(A^T) = \det(A) [/math]

Anonymous Sun Jan 21 20:38:02 2018 No.9453797

>>9453788
Oh and listen to the other guy.
Linear Algebra IS everything.
You don't know it extremely well, you are fucked, so learn it.
It's one of the simplest subjects out there, but a bad teacher or a bad textbook can definitely make it seem very hard.

>>	Anonymous Sun Jan 21 20:48:29 2018 No.9453808 >>9453659 what's an element of $X \times Y$?

>>	Anonymous Sun Jan 21 20:49:48 2018 No.9453810 >>9453713 That doesn't sound right. You combine them with k vector fields.

>>	Anonymous Sun Jan 21 21:01:16 2018 No.9453823 >>9453810 That's just for 1-forms.

>>	Anonymous Sun Jan 21 21:05:12 2018 No.9453827 >>9453810 ah nvm, you're right. But yeah basically you just integrate them.

>>	Anonymous Sun Jan 21 22:25:00 2018 No.9453915 File: 216 KB, 584x530, 1516498148559.jpg [View same] [iqdb] [saucenao] [google] Can someone pls just tell me quantum theory is just an elaborate prank

Anonymous Sun Jan 21 22:25:28 2018 No.9453916

How does one prove the following:

[math]
\text{If} \\
Z \sim N_n(0,I) \text{ (n-dimensional normal distribution with mean 0 and variance I )} \\
A \text{ is a symmetric n by n matrix of rank r} \\
\text{then}\\
Z'AZ \sim \chi_r^2 \text{, where} Z' \text{denotes the transpose of} Z \text{and} \chi_r^2 \text{ is the chi-square distribution with n degrees of freedom}
[/math]

>>	Anonymous Sun Jan 21 22:27:29 2018 No.9453919 >>9453916 I proved it in the case A has only the eigenvalues 1 and 0 (application of the real spectral theorem), but I can't find how to do it in general.

Anonymous Sun Jan 21 22:37:32 2018 No.9453933

>>9453916
>>9453919
Actually it's probably my textbook (linear modeling) being retarded. It skipped the proof and then applied it to prove this:
[math] \frac{SSE}{\sigma^2} \sim \chi_{n-p}^2 [/math] by writting [math] SSE=\varepsilon ' (I-H) \varepsilon [/math] (H is the Hat matrix).
[math] I-H [/math] is idempotent (and symmetric), which means that 0 and 1 are its only eigenvalues.

>>	Anonymous Sun Jan 21 22:44:16 2018 No.9453942 >>9453919 In general? If A is symmetric n by n of rank r, so is 2A. How can Z'AZ have the same distribution as Z'2AZ?

>>	Anonymous Sun Jan 21 22:51:39 2018 No.9453957 File: 14 KB, 698x93, Καταγραφή.png [View same] [iqdb] [saucenao] [google] >>9453942 True, it would follow pic related. Thanks for the counterexample!

Anonymous Mon Jan 22 01:13:48 2018 No.9454201
File: 119 KB, 707x764, We just don't know.png [View same] [iqdb] [saucenao] [google]

Hey /sci/, I don't often come here, but I'm going to defer to you guys.

I've been wanting to write a novel for some time, in a sci-fi setting and it has been going swimmingly developing it. But one aspect of the universe is how to make space combat interesting, and has some crucial plot points to it. In an effort to not have to resort to the 'hard' version seen in works such as The Expanse and The Forever War, I've wanted to have it more akin to 1800's naval warfare, where ships duked it out and pounded each other down.

To explain this, I've wanted a way to distribute kinetic energy. For example, a bullet impacting a kevlar vest distributes its impact force over a greater area through the fine mesh of fibers in the vest. I've wanted a relatively similar aspect for starship armor without going completely overboard with the handwaving.

I've tried to read up on how kinetic energy works, if it can be directed or harnessed, somewhat how we master electricity int today's world. If you had the alloy called Handwavium, what would its properties have to be like to be able to efficiently distribute kinetic energy throughout its surface area? Does kinetic energy travel at the speed of sound, light or the transference speed of its affected material?

tl;dr how kinetic energy work

>>	Anonymous Mon Jan 22 01:15:04 2018 No.9454204 >>9454201 On the point of researching the properties of kinetic energy myself, I forgot to add that the math is far above my head. If someone could explain it to me like I'm ten years old, that'd be awesome.

Anonymous Mon Jan 22 01:20:08 2018 No.9454212

>>9454204
If you stab a knife into a point it'll go in with the entire force concentrated to a single point. If you hit something with a force equal to the stab, not only would it not draw blood but it probably wouldn't even hurt that badly. The kevlar wrapped around the body changed that point of contact from a gunshot or stab from a pinpoint to a wide area by lateral diffusion (force sideways instead of force inwards). The molecular structure of kevlar makes this possible because the bonds are so rigid that pushing forwards on it causes force to be distributed through the material laterally. If you wanted to incorporate this into a sci-fi story you could use the same principles but for a shield surrounding the ship instead of a person wearing a vest.

>>	Anonymous Mon Jan 22 01:21:24 2018 No.9454213 File: 4 KB, 200x133, download.jpg [View same] [iqdb] [saucenao] [google] >>9450832 If theory of evolution is true, then why do single-celled animals & monkeys still exist?

Anonymous Mon Jan 22 01:25:51 2018 No.9454218

>>9454212
So there's no way to manipulate the way the energy interacts with the material? You can only diffuse it with different materials?

Maybe to better get across what I mean, you can channel electricity through conductors on a motherboard. There is no way to manipulate kinetic force in a similar way?

Anonymous Mon Jan 22 01:42:00 2018 No.9454232

>>9454218
There are ways, but in talking about them we'll just convolute the whole purpose of your post which was to make the idea simpler. Energy can be converted from one form into another through a whole variety of mean. In the kevlar-stab-wound example we aren't converting anything, just changing the size of the surface over which that energy is distributed. But if you wanted to talk energy weapons in a sci-fi setting, kinetic energy could be dissipated as heat in a non-harmful conversion. If waves were involved, waves of a certain wavelength could be converted to a non-harmful wavelength by diffraction or destructive interference.

If we're sticking strictly to kinetics and you want to convert kinetic energy into something else, you need moving parts, like shock absorbers. If you strike something and it is allowed to move, the movement will decrease the impact on the stationary parts, and I might be wrong but this sounds like more the direction you would want to go.

>>	Anonymous Mon Jan 22 01:44:57 2018 No.9454239 >>9454213 This is the stupid questions thread, not the shitposting questions thread

>>	Anonymous Mon Jan 22 02:14:11 2018 No.9454264 >>9454239 A middle-aged man asked me this question once, & I had a hard time explaining. He was smiling, too.

Anonymous Mon Jan 22 02:24:53 2018 No.9454281

>>9452826
>Young and Freedman - University Physics with Modern Physics
Yes all of it from the very beginning. Classical Mechanics is still valid (and forms the basis of future discussion) and didn't go away like alchemy.

Then
http://4chan-science.wikia.com/wiki/Physics_Textbook_Recommendations#Special_Relativity
http://4chan-science.wikia.com/wiki/Physics_Textbook_Recommendations#Quantum_Mechanics

>>	Anonymous Mon Jan 22 02:26:11 2018 No.9454282 >>9452857 http://4chan-science.wikia.com/wiki/Universal_Material#Technical.2C_Scientific.2C_and_Mathematical_Writing

Anonymous Mon Jan 22 02:38:42 2018 No.9454291
File: 32 KB, 655x641, double integral.png [View same] [iqdb] [saucenao] [google]

Can anyone explain this example to me? I don't understand the last equation. I get the 2(x^2+y^2) as that is the jacobian determinant, but where does the 'times a half ' come from?

>>	Anonymous Mon Jan 22 02:48:34 2018 No.9454296 >>9454291 1/2*2=1

>>	Anonymous Mon Jan 22 02:50:35 2018 No.9454298 >>9453039 http://4chan-science.wikia.com/wiki/Programming_Textbook_Recommendations#Haskell

>>	Anonymous Mon Jan 22 02:51:11 2018 No.9454299 Can someone give me a hint on how to prove this? Let [math] n,r \in mathbb{N}[/math] Show [math] r! \mid (n+1)(n+2) \cdots (n+r) [/math] Looks like a rising factorial but not sure how to proceed?

>>	Anonymous Mon Jan 22 02:56:58 2018 No.9454305 >>9454291 You're about to rip out a correction factor dudv=2(x^2+y^2)dxdy = ∯1/2 dudv = 3

>>	Anonymous Mon Jan 22 02:56:59 2018 No.9454306 >>9454299 The easiest way is giving a combinatorial argument: You know that (n+r) choose r is [math] \frac{(n+1)...(n+r)}{r!} [/math]. And the binomial coefficients are integers, so the denominator must divide the numerator.

>>	Anonymous Mon Jan 22 02:58:56 2018 No.9454308 >>9454299 n+r choose r is an integer. QED

>>	Anonymous Mon Jan 22 03:06:21 2018 No.9454310 >>9454308 >>9454306 garbage "proofs"

>>	Anonymous Mon Jan 22 03:21:29 2018 No.9454320 >>9454310 It essentially is the same as proving (n choose k) = (n-1 choose k) + (n-1 choose k-1) but multiplied by k! https://math.stackexchange.com/a/12121

>>	Anonymous Mon Jan 22 08:07:28 2018 No.9454596 >>9452530 thanks man

BA EE Mon Jan 22 09:12:05 2018 No.9454667

>>9450832
im at the end of my sophmore year of getting my bachelors degree in Electrical engineering. anybody here working as one? whats it like?
many of my friends are switching to mechanical because they didint like what they learned in phys 2, but ive been planning to be an EE my whole life. how is it?

>>	Anonymous Mon Jan 22 10:16:22 2018 No.9454713 >>9452883 pls respond

Anonymous Mon Jan 22 10:26:01 2018 No.9454727

>>9454667
Hey EE student here too, can you help me with something:

For an electrostatic actuator, am I correct in thinking V should stay in between V_pull_in and V_pull_out?

If you don't know/use these last 2 terms. They are defined in this paper:
https://paginas.fe.up.pt/~larocha/articles/MME02.pdf

>>	Anonymous Mon Jan 22 17:10:06 2018 No.9455200 >>9454281 Thank you, I'm currently reading the Feynman lectures that were on the /sci/ wiki, should I put that on pause and read Young and Freedman first? Feynman is going through the very basics first but it is very extincive and comprehensive

>>	Anonymous Mon Jan 22 21:01:45 2018 No.9455338 best combinatorics book out there incl. problems with full solutions/proofs ?

>>	Anonymous Mon Jan 22 23:24:04 2018 No.9455387 >>9452385 >saw it in Reddit >he’s the cuck

>>	Anonymous Mon Jan 22 23:30:43 2018 No.9455389 >>9452385 >saw it in Reddit >he’s the cuck

Anonymous Tue Jan 23 00:07:53 2018 No.9455395

>take differential equations
>get an A
>take principles of electronics, class on circuits and whatnot
>get an A
>first lab of semester
>easy as fuck circuit
>no one can even read the circuit diagram except me
>people taking pictures of circuit to "remember it"
Is this going to be an easy A? In my differentials class, we did equations on circuits already. Is this pretty much it?

Anonymous Tue Jan 23 00:47:12 2018 No.9455403

If I know how to read circuit diagrams and solve differential equations, will Physics: Electricity and Magnetism be easy?
First lab was just putting together an easy as fuck circuit, which most of everyone in the class couldn't even read.
I had an A in differentials and a lot of times I was supposed to solve circuits using methods on how to solve its differential equation.

>>	Anonymous Tue Jan 23 03:42:57 2018 No.9455421 test

>>	Anonymous Tue Jan 23 07:30:20 2018 No.9455518 >>9455403 Yes. The E&M is hard meme is from turbo brainlets.

>>	Anonymous Tue Jan 23 07:41:57 2018 No.9455528 >>9455403 As far as I remember the hardest part in my course was some ugly integrals with retarded time and weird geometry and some boring field theory. Depends on the prof I guess

>>	Anonymous Tue Jan 23 08:08:17 2018 No.9455546 Am I retarded?

>>	Anonymous Tue Jan 23 08:13:38 2018 No.9455554 >>9455546 no no

>>	Anonymous Tue Jan 23 20:32:52 2018 No.9456592 >>9450874 mary boas - mathematical methods in the physics sciences >chapter 1 should review what you want

>>	Anonymous Tue Jan 23 20:34:34 2018 No.9456596 I feel overwhelmed with course credit hours and research. will i adapt to the load? or be miserable for the rest of this semester >inb4 brainlet

>>	Anonymous Tue Jan 23 20:38:14 2018 No.9456604 >>9456596 That's a question only you can answer. It's entirely possible to stay sane under literal torture, but it's a case by case basis.

>>	Anonymous Tue Jan 23 20:41:38 2018 No.9456611 >>9456604 thank you desu, i will evolve and maintain sanity

>>	Anonymous Wed Jan 24 09:24:31 2018 No.9457587 Why does aluminum foil burn in a microwave? I thought carbon is needed to created the co and co2 that generates flames, is there enough carbon in aluminum foil and that's why it burns or does aluminum itself burn?

>>	Anonymous Wed Jan 24 09:35:04 2018 No.9457596 Engineering degree tier list?

>>	Anonymous Wed Jan 24 11:30:42 2018 No.9457768 >>9451335 >>9451341 Easy [math] \sum_{k=1}^n \lg n - \sum_{k=1}^n \log k = n \log n - n \log n + n - O(\log n) = O(n) [/math]

Anonymous Wed Jan 24 11:32:25 2018 No.9457774

>>9457587
CO en C02 don't generate flames!, they are byproducts from burning
(simplified) C +02 -> CO2 + heat

CO is dangerous to humans an is a byproduct burning C with too little O
(simplified) C + O -> CO + heat

The flame is the heat. CO and CO2 are the smoke.

You can burn (in the way you mean it) other things than C too, you just have to have
>enough energy to create a spark
>O2 to make a flame
>some feeding material that interacts with the O2 and that spreads the interaction after an initial spark

>>	Anonymous Wed Jan 24 11:33:59 2018 No.9457778 I don't understand why the energy bands at a hetero-junction makes this* assymptote-like shape at a hetro-junction. What's the reasoning behind this? *https://youtu.be/fKCWl1tpBys?t=5m13s

Anonymous Wed Jan 24 19:34:33 2018 No.9458687

>>9457774
Thanks I think my autism can live at ease now, I don't fully understand electromagnetism yet and the buzzfeed tier articles I could find online only talked about the part where aluminum foil being the spark, but this is the information I was looking for, much more insightful lol

I also love the enthusiasm

>>	Anonymous Wed Jan 24 19:44:20 2018 No.9458707 File: 21 KB, 600x647, 4ab.jpg [View same] [iqdb] [saucenao] [google] If 1 cm is 10 mm, and that's 10000 micrometers, what are the units in between? Like the 100ths and 1000ths?

>>	Anonymous Wed Jan 24 20:02:44 2018 No.9458740 File: 16 KB, 722x48, Capture.png [View same] [iqdb] [saucenao] [google] help me evaluate this bros

>>	Anonymous Wed Jan 24 20:27:12 2018 No.9458798 >>9453567 I could give you the exact definition, but as a lowly engineer I couldn't possibly teach something to such a brilliant and vastly superior mind like yourself. Idiot.

Anonymous Wed Jan 24 20:27:22 2018 No.9458799

Is there any other good physics lectures besides the ones with Walter Lewin? I'm self studying physics with Halliday book and some good lectures would be great. I like the experiments Lewin makes in the lectures, but he often skips some topics here and there.

I tried Young. Good book, but some chapters are unnecessarily long.

Pls no bulli

>>	Anonymous Wed Jan 24 20:28:14 2018 No.9458801 >>9452965 Do you mean review papers?

>>	Anonymous Wed Jan 24 20:29:50 2018 No.9458805 >>9451700 >>9451707 >not having memorized pi up the 100 digits just for fun

>>	Anonymous Wed Jan 24 20:32:33 2018 No.9458812 >>9458798 He is asking this to mathematicians, you fucking brainlet. He asking about DoF of random variables anyway, not DoF of retarded engineering mechanical rotations n shit.

>>	Anonymous Wed Jan 24 20:32:54 2018 No.9458815 >>9458799 Read Giancoli's Physics for Scientists & Engineers.

>>	Anonymous Wed Jan 24 20:35:20 2018 No.9458826 >>9458812 Yeah right, "he". PS: I literally learned about the degrees of freedom of a random variable in my freshman year. I use random variables literally all the time. Stop embarrassing yourself.

>>	Anonymous Wed Jan 24 20:44:46 2018 No.9458850 I'm a senior humanities student and want to change my major to math. Is this stupid? Ive taken Calc 1, 2 and this class called Intro to Advanced Math

>>	Anonymous Wed Jan 24 21:01:02 2018 No.9458882 File: 907 KB, 2592x1944, IMG_20180124_205956.jpg [View same] [iqdb] [saucenao] [google] How do I know when a linear algebra matrix is "done" for infinite and no solutions?

>>	Anonymous Wed Jan 24 22:45:25 2018 No.9459081 ChemE or Petroleum Engineering?

>>	Anonymous Wed Jan 24 23:49:20 2018 No.9459222 ww

>>	Anonymous Thu Jan 25 00:00:04 2018 No.9459241 >>9458707 I'm not entirely sure what you're asking. Are you asking what the different SI prefixes are? https://en.wikipedia.org/wiki/Engineering_notation#Overview

>>	Anonymous Thu Jan 25 00:05:34 2018 No.9459248 File: 1.87 MB, 4032x3024, 7BB10ADF-38F7-4024-8B48-533FE838F76F.jpg [View same] [iqdb] [saucenao] [google] >x and y conponents How do I do this? Basically the (x,y) coordinates? they dont even list the charge so I’m confused

>>	Anonymous Thu Jan 25 00:11:46 2018 No.9459257 >>9459248 Is magnitude the same as the x and y components? So should I use F = K(q)(q_1)/r^2

>>	Anonymous Thu Jan 25 00:14:31 2018 No.9459261 Here's a stupid question: how do you catch up in school once you've fallen behind? Or do you have to just eat it every time?

>>	Anonymous Thu Jan 25 01:08:31 2018 No.9459327 why do all my western blots come out like ass

Anonymous Thu Jan 25 02:28:01 2018 No.9459415
File: 13 KB, 469x165, problem.png [View same] [iqdb] [saucenao] [google]

This is for a statistics class by the way.

I've seen a solution to similar problem that results in the left hand being LESS THAN 1/8 with the constraints being x + y + z = 1 and x,y,z > 0.

In that solution the fact that the Arithmetic mean is greater than the geometric mean is used to prove the equation. I've tried a few things, but everything I try seems to take me further away from the solution.

>>	Anonymous Thu Jan 25 04:35:06 2018 No.9459508 >>9450896 for an intuitive understanding of calculus check out this guy's yt channel. He has a playlist called "the essence of calculus" https://www.youtube.com/channel/UCYO_jab_esuFRV4b17AJtAw Recommended

>>	Anonymous Thu Jan 25 04:47:14 2018 No.9459516 >>9455387 >>9455389 >posts twice what a cuck

>>	Anonymous Thu Jan 25 04:49:18 2018 No.9459519 Is it too late to study in 24yo?

>>	Anonymous Thu Jan 25 07:42:29 2018 No.9459624 >>9459519 >Is it too late to study in 24yo? No.

>>	Anonymous Thu Jan 25 07:43:00 2018 No.9459625 >>9459516 >>posts twice what a cuck Who are you quoting?

>>	Anonymous Thu Jan 25 08:42:03 2018 No.9459668 >>9459241 Yeah like 10 cm is a decimeter, what's a 100th of a cm called

>>	Anonymous Thu Jan 25 10:20:43 2018 No.9459823 >>9458798 Hey, smart guy, I came up with this one >>9458683 . Is it correct?

Anonymous Thu Jan 25 10:30:16 2018 No.9459847
File: 868 KB, 1000x1000, OPCHdS4.png [View same] [iqdb] [saucenao] [google]

>>9451002
I'm not sure if we're referring to the same thing necessarily, but I was taught that "anti derivative" was a function which produced a function in the "opposite direction", abstractly speaking. Whereby 2x can be brought to x^2 +c using a "anti derivative" , C being the possible constant loss of a constant when a function is derived.
It is an anti derivative because it actually can undo the transformation made by differentiation.

>>	Anonymous Thu Jan 25 10:32:55 2018 No.9459854 >>9459847 autismo correction 2x becomes 1/2x^2 + c using an indefinite integral

>>	Anonymous Thu Jan 25 11:21:37 2018 No.9459942 >>9459081 ChemE

>>	Anonymous Thu Jan 25 11:25:02 2018 No.9459945 >>9459854 >autismo correction 2x becomes 1/2x^2 + c using an indefinite integral The original was correct

>>	Anonymous Thu Jan 25 11:33:50 2018 No.9459963 How would I show an automorphism group of a cyclic group is isomorphic to a smaller cyclic group? I know the order is the same.

>>	Anonymous Thu Jan 25 11:34:50 2018 No.9459967 >>9459963 If the order is the same why would it be isomorphic to a smaller group?

>>	Anonymous Thu Jan 25 11:36:22 2018 No.9459973 >>9450972 Yes, but only if you add a term in [math]\mathbf F[/math] that corresponds to non-inertial forces.

>>	Anonymous Thu Jan 25 11:48:12 2018 No.9459998 >>9459261 Weekends, evenings, lunch, most free time you have that is NOT sleep (please fucking sleep you need it so much) is now dedicated to the professor, lecture vids, and catching up.

>>	Anonymous Thu Jan 25 11:54:26 2018 No.9460010 >>9459967 The order of the automorphism group is the same as the order of the smaller group.

>>	Anonymous Thu Jan 25 11:56:53 2018 No.9460012 >>9460010 >The order of the automorphism group is the same as the order of the smaller group. What smaller group?

>>	Anonymous Thu Jan 25 12:01:41 2018 No.9460031 What is the principal structural difference between cellulose and glycogen and why don't we have the enzyme to break down cellulose?

>>	Anonymous Thu Jan 25 13:12:54 2018 No.9460202 >>9457778 bump

Anonymous Thu Jan 25 14:08:15 2018 No.9460318

How do you calculate the average slope m of a probability function in a given interval difference deltax (meaning that it could be any x value for x1 or x2 if deltax is x2-x1) ?
So for example, if y = 3 or 4 has a probability of 25%, y = 5 or 2 14%, y = 6 or 1 6%, y = 7 or 0 1%, and the function can only grow of 1y per 1x, how would I calculate the absolute average slope of, say, an interval of deltax = 2 ?

Anonymous Fri Jan 26 07:09:29 2018 No.9462133

>>9452826
You can not understand ANY physics without understanding the math. The math is the model. The model explains the physical event. Watching stupid "wowsodeep cat is alive and dead xDDD" youtube videos does NOT make you better in physics. It just gives you the illusion of having learned something which in reality you don't understand at all.

If you really want to start learning read something like Giancoli's physics for scientists and engineers.

>>	Anonymous Fri Jan 26 07:49:58 2018 No.9462174 My professor is fucking my ass incredibly hard on intro to fluid mechanics course. Please recommend me a good set of lectures, solved examples and problems. I don't want to fail this course ;_;

>>	Anonymous Fri Jan 26 10:43:03 2018 No.9462495 >>9462133 Physics? Kleppner's Mechanics and Purcell's Electricity and Magnetism or Griffith's Electrodynamics. Griffiths also has Quantum I think and is commonly assigned. Also Shankar.

>>	Anonymous Fri Jan 26 10:46:10 2018 No.9462500 What is the most basic level at which linear algebra begins to link to probability and statistics?

Anonymous Fri Jan 26 10:51:23 2018 No.9462511

>>9462500
>What is the most basic level at which linear algebra begins to link to probability and statistics?
What do you mean by "link"? The most basic application I can think of where you apply linear algebra to something involving probability is with Markov chains
https://en.wikipedia.org/wiki/Examples_of_Markov_chains

>>	Anonymous Fri Jan 26 11:48:41 2018 No.9462611 File: 795 KB, 2048x1152, 20180126_104717.jpg [View same] [iqdb] [saucenao] [google] I have to prove L(sint) = 1/(x^2 + 1), what's the next step here?

Anonymous Fri Jan 26 12:16:50 2018 No.9462665

>>9451535
[math]2^1 = 2*2^0 = 2^0 + 2^0[/math]
[math]2^2 = 2*2^1 = 2^1 + 2^1 = 2^1 + 2^0 + 2^0[/math]
[math]2^3 = 2*2^2 = 2^2 + 2^1 + 2^0 + 2^0[/math]
...
[math]2^n = \sum\limits_{k=0}^n 2^k + 2^0[/math]
Subtracting 2^0 = 1 from the last equation gives:
[math]2^n - 2^0 = 2^n - 1 = \sum\limits_{k=0}^n 2^k[/math]

>>	Anonymous Fri Jan 26 12:17:32 2018 No.9462668 >>9462611 Substitute the limits for t (0 and \infty) like you usually do while integrating by parts.

>>	Anonymous Fri Jan 26 15:09:19 2018 No.9462978 File: 354 KB, 1920x1440, 27335448_1777645262285679_1032976904_o.jpg [View same] [iqdb] [saucenao] [google] What is Q1 actually asking? How am I supposed to answer it like?

>>	Anonymous Fri Jan 26 15:11:23 2018 No.9462985 >>9462978 Explain what it means for two functions to be equal and show G is a group

>>	Anonymous Fri Jan 26 15:23:56 2018 No.9463005 >>9462978 It wants a definition of equality for functions. You want to write something along the lines of "f = g if and only if <something>".

>>	Anonymous Fri Jan 26 15:25:18 2018 No.9463010 File: 34 KB, 1125x379, .png [View same] [iqdb] [saucenao] [google] I think I am legitimately retarded. What do I actually do to get there?

Anonymous Fri Jan 26 15:33:34 2018 No.9463026

>>9450832
Here is a stupid question.
[math]\text{Let }X \text{ be a non-empty compact Hausdorff space }[/math]
[math]\text{and a map }f:X\rightarrow X \text{ be continuous.}[/math]
[math]\text{By definition, put } X_1 = X \text{ and } X_{n+1} = f(X_n)\text{ inductively for all } n\in \mathbb{N}.[/math]

[math]\text{Prove that }A = \bigcap_{n=1}^\infty X_n \text{ is non empty}[/math]

>>	Anonymous Fri Jan 26 15:34:36 2018 No.9463028 >>9463026 The question being, can someone do this homework for me

>>	Anonymous Fri Jan 26 15:46:23 2018 No.9463058 File: 23 KB, 931x389, 53.png [View same] [iqdb] [saucenao] [google] >>9463010 I think I did it? Not sure if I did something wrong. Feels like too much of a step to just leave out of the solutions as well.

>>	Anonymous Fri Jan 26 15:48:26 2018 No.9463060 >>9463026 what do you know about intersection of centered families of closed subsets in a compact space ?

>>	Anonymous Sat Jan 27 07:49:00 2018 No.9464627 >>9462985 >>9463005 And for the second part is it showing that the operation (f+g)(x) is a group?

Anonymous Sat Jan 27 09:01:52 2018 No.9464768

>>9460031
The anomeric hydroxyl groups in the glucose monomers in glycogen are in the alpha conformation (1 axial), while those in cellulose are in the beta position (all equatorial). Glycogen exists as branched spirals, since the conformation has a slight curve overall. Cellulose is flat, since all hydroxyl groups lie in the same plane.

>>9451187
Ikr?! The knot is larger than his lips, and the lapels are to narrow for that tie

>>	Anonymous Sat Jan 27 09:12:06 2018 No.9464783 Hello /sci/, I'm on that time series shit right now I gotta show that [math]\sum_{i \neq j} x_ix_j \leq \sum_{i=1}^{n} x_i^2 /[math] for [math]i,j=1,...,n/[math] Should I go by induction or somehow make use of Cauchy Schwarz ? Ty in advance

>>	Anonymous Sat Jan 27 09:13:39 2018 No.9464786 Hello /sci/, I'm on that time series shit right now I gotta show that [math]\sum_{i \neq j} x_ix_j \leq \sum_{i=1}^{n} x_i^2 [/math] for [math]i,j=1,...,n[/math] Should I go by induction or somehow make use of Cauchy Schwarz ? Ty in advance

>>	Anonymous Sat Jan 27 09:16:26 2018 No.9464793 >>9464786 PS this might not be true but it would really help if it were

>>	Anonymous Sat Jan 27 09:27:44 2018 No.9464810 >>9464786 WIth no other information than that the x_i are real numbers? False in general. if the x_i are all equal to 1, the sum on the left is n(n-1) and the sum on the right is n. For n>2, n(n-1) > n.

>>	Anonymous Sat Jan 27 09:46:38 2018 No.9464840 >>9464810 yeah x_i are real also wow thanks, surprised I missed such a trivial counterproof i feel dumb now

Anonymous Sat Jan 27 09:46:45 2018 No.9464841

>>9454667
Same boat. Thermo was my favourite unit in chemistry and knowing that mech kids get to take a bunch of classes on that while we only get one is a bummer. I'm hesitant about going into MechE since everything is moving towards Digital electronics.

>>	Anonymous Sat Jan 27 10:11:16 2018 No.9464880 How do i solve for B? \begin{equation} \begin{vmatrix} 1 & 2 \\ 2 & 3 \\ 3 & 4 \end{vmatrix} \cdot B = \begin{vmatrix} 1 & 5 & 1 & -2 \\ 3 & 8 & 4 & -1 \\ 5 & 11 & 7 & 0 \end{vmatrix} \end{equation}

>>	Anonymous Sat Jan 27 10:51:33 2018 No.9464967 >>9464880 Row operations on both sides to reduce the nameless matrix on the left-hand-side to 1 0 0 1 0 0 Then the solution should be obvious.

>>	Anonymous Sat Jan 27 12:27:08 2018 No.9465181 File: 23 KB, 480x360, hqdefault.jpg [View same] [iqdb] [saucenao] [google] >>9450832 >uses sin^-1(x) >spots arctan afterwards in the text >conclusion: solve for exponential of sin x >turns out it was for arcsin why do people do this

>>	Anonymous Sat Jan 27 15:02:48 2018 No.9465562 Can someone explain to me why given: y' = x^2 - y^2 y'' = 2x - 2yy' ?

>>	Anonymous Sat Jan 27 15:04:59 2018 No.9465570 >>9465562 Just take the derivative of each side.

>>	Anonymous Sat Jan 27 15:09:18 2018 No.9465577 >>9465570 Could you show me the passages? Because I don't think I know how to do it since I studied until partial derivatives.

>>	Anonymous Sat Jan 27 15:10:22 2018 No.9465581 >>9465577 I meant the steps oops

>>	Anonymous Sat Jan 27 15:10:37 2018 No.9465583 >>9465577 You use the power rule on x^2 and the chain rule on y^2

>>	Anonymous Sat Jan 27 15:14:42 2018 No.9465596 What are the prereqs for me to learn how to do Regression? It's the only thing from statistics that I care about. Can I learn about it as-is? My highest maths is calculus 2

>>	Anonymous Sat Jan 27 15:16:36 2018 No.9465601 >>9465583 I know both of those rules but I do not know how to do it in this case. It's a derivative with respect to what?

>>	Anonymous Sat Jan 27 15:17:26 2018 No.9465603 >>9465601 >It's a derivative with respect to what? x

>>	Anonymous Sat Jan 27 15:17:56 2018 No.9465604 >>9465596 >Can I learn about it as-is? Yes.

>>	Anonymous Sat Jan 27 15:19:21 2018 No.9465611 >>9465604 do you have any good reading material anon? I'd kahn academy that shit but he jumps a lot and I just want to know know about this particular subject.

>>	Anonymous Sat Jan 27 15:21:57 2018 No.9465620 >>9465603 I see. What is causing problems is that usually, I have something like f(x,y) = x^2 - y^2 so f'(x,y) w.r.t. x = 2x basicly: why can't I treat y as a constant in this case if the derivative is w.r.t. x?

Anonymous Sat Jan 27 15:25:52 2018 No.9465630
File: 54 KB, 1169x758, 3.png [View same] [iqdb] [saucenao] [google]

I don't really get how I'm supposed to deal with recursion. My textbook just says insert into itself and then gives me the solution but I don't get how I'm supposed to eliminate the recursion. I guess I am supposed to see a pattern or something but I am just too much of a brainlet to figure this out.

>>	Anonymous Sat Jan 27 15:26:06 2018 No.9465632 >>9465620 >basicly: why can't I treat y as a constant in this case if the derivative is w.r.t. x? y is a function of x, so y'(x)=x^2-y(x)^2

>>	Anonymous Sat Jan 27 15:26:57 2018 No.9465639 >>9465630 >My textbook just says insert into itself Don't do that.

Anonymous Sat Jan 27 15:28:34 2018 No.9465644

Is there any difference between sticking a piece of hot food into a very well insulated container, or leaving it on a heated surface with sensors to maintain exactly the current temperature it is at?

My friend said the latter approach would scorch it since you're continually applying heat but I'd have thought it would be exactly the same, besides some potential moisture loss due to the second approach being open to the air rather than enclosed.

>>	Anonymous Sat Jan 27 15:28:50 2018 No.9465645 File: 58 KB, 701x411, 54.png [View same] [iqdb] [saucenao] [google] >>9465639 I don't get it then. It literally says "insert into itself" and then goes ・・・ What do I actually do to get to the result?

>>	Anonymous Sat Jan 27 15:33:45 2018 No.9465663 >>9465632 Oh, I see. so y(x)^2 becomes 2y*y' where y(x) is g(x) and f(g(x))=y(x)^2 Thank you!

>>	Anonymous Sat Jan 27 15:39:35 2018 No.9465683 >>9465645 >What do I actually do to get to the result? Induction.

>>	Anonymous Sat Jan 27 15:40:38 2018 No.9465687 >>9465683 Sorry I'm a first semester business computer science student, I don't think this is on the curriculum.

>>	Anonymous Sat Jan 27 15:41:49 2018 No.9465689 >>9465687 look if p_1 holds true if it does, assume p_k holds true then, show p_k+1 holds true not rocket science

>>	Anonymous Sat Jan 27 15:44:30 2018 No.9465696 >>9465689 But I am not trying to prove a statement, I am trying to eliminate the recursion, right?

>>	Anonymous Sat Jan 27 15:47:54 2018 No.9465706 >>9465696 Not that guy, but you don't get proof by induction. If you prove it holds for k=1 and you proof that if it holds for k, then it also holds for k+1. Then you have proved it for any natural k, do you see?

>>	Anonymous Sat Jan 27 15:49:30 2018 No.9465707 >>9465706 Yea, but I'm not trying to prove anything.

>>	Anonymous Sat Jan 27 15:50:24 2018 No.9465709 >>9465707 >Yea, but I'm not trying to prove anything. Then what are you doing?

>>	Anonymous Sat Jan 27 15:50:45 2018 No.9465711 >>9465709 Trying to eliminate the recursion.

>>	Anonymous Sat Jan 27 15:51:56 2018 No.9465714 >>9460318 A slope is a differentiation of some function in respect to some variable, what variable do you want to differentiate in respect to?

>>	Anonymous Sat Jan 27 15:53:14 2018 No.9465716 >>9465711 >Trying to eliminate the recursion. You do that by induction.

>>	Anonymous Sat Jan 27 15:57:35 2018 No.9465730 >>9465645 >then goes ・・・ This is a meaningless notion.

Anonymous Sat Jan 27 15:59:38 2018 No.9465734

>>9465644
It is definitely different in general because of air and convection, pressure, evaporation, etc, but I am assuming you mean in regards to temperature alone?

I have no idea about the chemical processes going on when meat goes bad, but it is reasonable to think there could be processing going on turning chemical energy into kinetic energy. Which would mean (in theory) insulating doesn't necessarily mean keeping temperature constant over long periods. In reality there is obviously also not a perfect insulator so you will have losses.

Anonymous Sat Jan 27 16:11:41 2018 No.9465761

>>9465716
You know, I don't really care. I looked at it some more and it seems to make some vague sense now. I don't really like mathematics but our teacher just put all these exercises up for god knows what reason. I am a first semester in a non-math degree, you can't expect me to know all the crazy methods already.
And they don't actually, the exam is a digital exam and you are only able to put in full numbers into the answer boxes, meaning there won't be anything like this in the exam. Now, I understand the value of knowing how to do this, but I really don't care anymore!

>>9465730
I posted a picture accompanying what I said where the operation is shortened by three dots. Shouldn't be too confusing.

Anonymous Sat Jan 27 16:17:39 2018 No.9465773
File: 62 KB, 400x400, points.png [View same] [iqdb] [saucenao] [google]

Suppose I want to pick random points in a disc. I have a function which does this. It makes them by selecting a random point on the radius and a random angle, but the random point on the radius is weighted by the square root function. Standard stuff you can find like I did by google.

Now suppose I want to find N such points, under the additional constraint that no point can be within [math]\delta[/math] of any already found point. Clearly if [math]\delta[/math] and N are large enough we will be unable to choose N points because the constraints are too tight.

But, given reasonable restrictions, say, [math]N = 20[/math] points with [math]\delta = \frac{3}{100}[/math] on a disc with radius 1, can we still say prior to any point being chosen that all points are equally likely to be chosen?

>>	Anonymous Sat Jan 27 16:41:07 2018 No.9465824 >>9465611 >>9465604 >>9465596 Bump

>>	Anonymous Sat Jan 27 17:31:15 2018 No.9465919 >>9465824 >bumping an autosage thread

>>	Anonymous Sat Jan 27 17:36:13 2018 No.9465932 >>9462174 I would suggest this: bitly/2DK1Guo

>>	Anonymous Sat Jan 27 18:39:18 2018 No.9466052 >>9465773 I doubt it. Points along the edge would be less likely to be excluded than the point in the middle. Just a first intuition.

>>	Anonymous Sat Jan 27 18:51:58 2018 No.9466072 >>9466071 >>9466071 >>9466071 >>9466071 NEW NEW >>9466071 >>9466071 >>9466071 >>9466071

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/sci/ - Science & Math