/sqt/ - Stupid Question Thread: Tuesday Edition

[join a secret society No.8986316]

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: >>8976643

[Anonymous No.8986488]

what's the most valuable degree? theoretical physics?
https://www.tcd.ie/courses/undergraduate/faculty/#F02

[Anonymous No.8986490]

What's the best text to learn measure theory? I have a copy of Folland

[Anonymous No.8986495]

I don't know if this is relevant here, but this is a medicine related question.
Last year around this time I got tested for about a million allergens since I had, for the first time in my life, a runny nose and itching eyes for no reason.
The tests came up with nothing, and it quickly went away.
Now, I'm experiencing the same damn thing. Anybody have any idea what it could be?

[Anonymous No.8986609]

Let's think of your average laser bolt from a video game weapon, say maybe the laser pistol from Fallout 3+. How hot is that bolt? If it hits somebody in the face, does the heat transfer to the person's body fluids and give them any sort of heat condition, if not outright boiling the cerebrospinal fluid and killing them?

Also, google won't tell me what temperature eyeballs melt at

[Anonymous No.8986860]

>>8986488
mathematical finance

>>8986490
Halmos/simon

[Anonymous No.8986910]

http://www.bbk.ac.uk/study/2017/undergraduate/programmes/UUBSPSAS_C/
http://www.openuniversity.edu/courses/qualifications/q64-ast
What can you do with a B.S. in Astronomy and Planetary Science?
Is it worth pursuing or should I focus on studying physics and later go into astrophysics if I'm into astronomy?

[Anonymous No.8986936]

>>8986316
I am a mathlet and need some resources to go from pre-algebra to competency in pre-calculus & trigonometry.

I've used Khan Academy before for their algorithm and into to compsci courses. I've been told their pure math stuff is good too. Any other suggestions?

[Anonymous No.8986941]

>>8986488
Biochemisty

[Anonymous No.8986946]

>>8986910
The earth flat moron. Now you know.

[Anonymous No.8986970]

How did they get the last expression?

[Anonymous No.8987075]

Explain information theory in 2000 characters or less to someone interested in the subject but too lazy to do his own research.

[Anonymous No.8987079]

>>8986941
seconded

[Anonymous No.8987107]

How do calculate whether or not a polygon is above or below a plane?

[Anonymous No.8987145]

I recently went on a diet high in iron (roughly 400% of the EU standards) and noticed that the metallic smell and taste of my blood was almost overpowering compared to before the diet.

Is it purely my imagination or are the two things related?

[Anonymous No.8987239]

Some years ago in my chemistry class my teacher did something i dont quite get.

He directed some flamable gas (i think it was hydrogen) through a glass tube and lighted it. Inside the glass tube was a metal looking like steel wool (might have been steel wool, though somehow i remember him noting on the side it was titanium?).
He said it prevents the flame from traveling down the tube, igniting the gas inside the tube as opposed to staying above the metal wool.

How does that work?

My only assumption is that its only about the texture of the metal wool making it "difficult" ?? for the flame to travel down past the metal wool, because the flow of the gas is so turbulant there and the passages between the threads of the wool are so thin that a flame somehow (but why) cannot form there.
The reason why it might have been titanium is because it wouldnt degrade as fast as eg iron.

[Anonymous No.8987278]

>>8987239
Fire needs oxygen, pure hydrogen won't burn alone. It has to oxidize ... the only other explanation is some fast moving air vortex shooting down the tube for whatever freak reason.

[Anonymous No.8987298]

>>8986488
Define value?
most fun?
most money?
highest potential for money?
if fun, depends on the shit you like doing
if money, Finance
most potential is Business, but that one is risky

[Anonymous No.8987338]

>>8987239
>>8987278
fire also needs heat energy wich fine metal fibers would absorp in case of backfire

[Anonymous No.8987429]

WTF why is differential equation modelling so fucking hard? I was trying to model a simple problem but every time I try I come up with a different, and wrong, answer. The problem is the following: suppose a petri dish filled with bacteria with uniform density. You inject the bacteria in the center with a virus. The virus spread only to those in contact with the infected bacteria after a fixed amount of time. What is the differential equation that relates the infected population with time (dP/dt)?

This looks pretty simple, the area of the infected population grows with its perimeter, which relates to the population by the density:

[math] \frac{dP}{dt}=2 \pi r [/math]
[math] P=\rho \pi r^2(t) [/math]
[math] \frac{dP}{dt}=\frac{dP}{dr} \frac{dr}{dt} = 2 \pi \rho r(t) \frac{dr}{dt}[/math]
[math] \frac{dr}{dt}=\frac{1}{\rho} [/math]
[math] r=\frac{t}{\rho}+c_{1} [/math]
[math] P=\pi(t+c_{1})^2 [/math]

Which sounds alright, a quadratic equation. But when I try to put in the speed at which the infection spreads, it all goes to shit. So, now, the rate at which it grows is proportional to the number of bacteria in the ring with thickness v:

[math]C: r_{0}<r<r_{0}+v [/math]
[math]A_{C} = \pi [(r+v)^2-r^2]=\pi(2rv+v^2) [/math]
[math]\frac{dP}{dt}=\rho A_{C}= \rho \pi(2rv+v^2)[/math]
[math]\frac{dP}{dr}\frac{dr}{dt}=2\pi\rho r\frac{dr}{dt}[/math]
[math]\frac{dr}{dt}= \frac{2rv+v^2}{2r}[/math]

To which the solution involves the Lambert-W and graphs nothing like I wanted (it is negative). I've also tried many other alternatives, trying to match units using dimensional analysis, nothing helps. Any help? Is there a book that will help me git gud?

[Anonymous No.8987438]

>>8986316
Should I apply to the CUKC program? I wouldn't wanna miss out on the CUKC experience.

[Anonymous No.8987455]

Is the HP50g just as powerful as a TI89 Titanium?

I'm an 2nd year ME who needs more power than my TI84 can deliver and I would love to try out an HP, but I'm on the fence over the fact of which one is able to accomplish more.

Or am I missing out on another option?

[Anonymous No.8987468]

>>8987145
Why the fuck are you tasting and smelling your own blood on such a regular interval that you can accurately track this bull shit.

No - and go outside and get some friends you goddam pyschopath

[Anonymous No.8987562]

>>8986495

A cold?

[Anonymous No.8987574]

Fucked myself and only have a couple days before first automata theory test. (Took it in the summer)

Been working full-time just to pay for the class and haven't opened the textbook. How fucked am I lads give it to me straight?

[Anonymous No.8987863]

For an arbitrary AVL tree the following holds:
[math]M(h)≤n [/math], where n is the number of nodes and h is the height of the tree
[math]M(h)=−1+\frac {5−2\sqrt 5}{5} r_{n}^{h}+\frac {5+2\sqrt 5}{5} r_{p}^{h}[/math]
and [math]r_{n}=\frac{1−\sqrt 5} {2},r_p=\frac{1+\sqrt 5} {2}[/math].

Show that for an arbitrary AVL tree holds: [math]h≤ \log_2 (n)∗1.44+const[/math]

I'm pretty sure it's impossible and our prof made a mistake when calculating his solution (the TA could not solve it)

[Anonymous No.8987947]

How do I get better at proofs? I failed my exam and have to resit it. I'm studying hard af but still am dying.

[Anonymous No.8987954]

Is mathematica useful for higher maths? Like analysis n' shit?
And for physics?

[Anonymous No.8987981]

I am doing this problem
1) Prove there are no positive integers satisfying x^2 + x = 4y^2 + 4y
2) Prove there are infinitely many rational solutions

I did part 1 but I am stuck in 2. But I have reduced it to finding rational points in the hyperbola y^2 = x^2 + x + 1

But how do I find rational points here? I have tried some substitution but nothing works. Any resources that could help me do this? It is the first time I do this kind of problem.

[Anonymous No.8988001]

Redpill me about philosophy, /sqt/.

[Anonymous No.8988036]

>>8987981
how did you reduce it? there's two integer points (-1,1) and (-1,-1) on your reduced curve

[Anonymous No.8988050]

What's some recommended basic lab equipment that's recommended for a beginner to buy outright? The sort of stuff that's better not to substitute.

I've had a bit of an interest in learning about basic chemistry recently, I guess mainly organic chemistry. Watching YouTube channels like NileRed, Cody's Lab, some explosives and energetics channels, as well as some MIT lab procedure stuff.

Initially, I'm just planning on doing some really basic stuff, build up a supply of useful reagents, solvents, or what have you, especially stuff I can't simply buy, because #lol meth and/or terrorism. My first experiment I have planned is just getting sulfuric acid from copper sulphate, because you can't easily buy sulphuric acid here. Waiting on a platinum electrode that's coming in the mail for that. Next, I might try burning elemental sulphur and passing it through water with a fish tank bubbler. Both of those are cheap and easy to get from gardening and nursery places. After that, I was thinking maybe nitric acid, distill water and ethanol, purify stuff like hydrogen peroxide, etc.

My draft list to start off with: a stand, burette, (Graham?) condenser, volumetric flask, and three-necked flask, and perhaps a handheld thermometer.

I figure then I can get a cheap cooking hotplate, some glass collection jars, a length of old duct and an exhaust fan for fumes, plastic tubing for joins, a few other secondhand bits and pieces that should be easy to find.

[Anonymous No.8988117]

>>8987863
Nevermind, it's trivial

[Anonymous No.8988168]

>>8988001
>Redpill me about philosophy, /sqt/.
They didn't advance so much until Galileo took the physics out of the cold hands of Aristotle and Russell took logic from the hand of Descartes.

[Anonymous No.8988169]

>get in huge argument with brainiac on /sci/
>get absolutely BTFO
>hide the thread
>entire rest of the day ruined

[Anonymous No.8988181]

>Took a seemingly legit IQ test based on raven's progressive matrices online
>10$
>115 IQ
>paid to find out I'm a brainlet

Can I complete my EE degree, /sci/entists?

I've seen seemingly dumber/average people do better than me in classes

[Anonymous No.8988183]

>>8986316
What should I learn to get a data science job after graduation?

[Anonymous No.8988185]

>>8988181
>IQ 115
I know that feel. Sorrow is indescribable. Like you lost everything and doomed to suffer for eternity.

[Anonymous No.8988209]

Seeking advice. I want the option for an easy return on investment from my undergraduate degree in mathematics, yet don't want to close the door for graduate school.

Should I, a) major in statistics and load up on pure math classes or b) major in pure math and take some statistics and probability classes?

[Anonymous No.8988217]

>>8988001
Gets shit on by shitty scientist and loved by fast food working idiots, but is completely worthwhile. Read some Russel, Popper, Khun and Heil at least.

[Anonymous No.8988219]

>>8988217
>Russel, Popper, Khun and Heil
why?

[Anonymous No.8988238]

>>8988183
Majoring in data science would be a decent starting point

[Anonymous No.8988239]

Why is bird poop white?

[Anonymous No.8988276]

>>8988238
I will get a bsc in maths and stats, and I dont have money for masters.

[Anonymous No.8988338]

I don't understand what I'm supposed to "describe" here.

[Anonymous No.8988340]

Which is the most difficult/advanced math branch with practical applications?

[Anonymous No.8988343]

>>8988338
describe the complementary graph...

i.e. the first one is just n points with no edges

[Anonymous No.8988357]

>>8988343
Ah ok, it sounded simple but I found the wording a bit too vague is all.
I'm guessing the second one is also just m+n vertices with no edges, right?

[Anonymous No.8988361]

>>8988357
>I'm guessing the second one is also just m+n vertices with no edges, right?
no, go take a look at what Kmn looks like again

[Anonymous No.8988376]

>>8988361
I'm stupid.
So from this I'm getting that instead of the n subset being connected to vertices in the m subset, it's connected to the other vertices in the same n subset; same applies for the m subset.
I think I got that correct now?

[Anonymous No.8988382]

>>8988376
>So from this I'm getting that instead of the n subset being connected to vertices in the m subset, it's connected to the other vertices in the same n subset; same applies for the m subset.
>I think I got that correct now?
yes

you could call it K_m disjoint union K_n or something

[Anonymous No.8988468]

I fell for the brainlet meme. How do I solve this(go over steps please). I solved with difference of squares and factorization, but ended up with 2u(probably an arithmetic error).

[Anonymous No.8988477]

>>8988382
Gotcha, thanks my dude.
Now I got up to this one but I don't really know what they want me to do.
Any tips?

[Anonymous No.8988485]

>>8988477
dawg it's literally the most natural ordering you can think of, just try writing out some adjacency matrices for small bipartite graphs

[Anonymous No.8988486]

>>8988468
Anons say its 4u, but they could've just been samefagging.

[Anonymous No.8988561]

>>8988485
I wasn't sure what they were on about with the rectangular blocks, but I drew a quick 4 vertices bipartite like a hourglass and made the adjacency matrix, and noticed what they meant.
Thanks senpai.

[Anonymous No.8988578]

I got 15/8 sec for the answer, yet when I look at the answer in the back it says the answer is 25/8 sec. What's the actual answer?

[Anonymous No.8988592]

>>8988578
how did you get 15/8

[Anonymous No.8988605]

>>8988592
Thought it said 2/3 ft/sec instead of 2/5 ft/sec.

[Anonymous No.8988612]

>>8988578
(5/4) ft / (2 ft / 5 sec) = ?

[Anonymous No.8988698]

>>8988578
(5 / 4) ft * (5 / 2) sec / ft

25 / 8 sec

[Anonymous No.8988705]

What is the quickest way to learn German? My primary language is English and I can roughly communicate in Spanish and Latin. Just trying to learn the language so I can move to Switzerland for PhD.

[Anonymous No.8988706]

>>8988705
german's a dying language, just learn arabic instead

[Anonymous No.8988712]

>>8988705
Move to Switzerland first with an English speaking job, learn German as you go

or

Do your PhD in Switzerland in English-e.g. ETH Zürich PhD programmes are in English

[Anonymous No.8988721]

>>8988578
D = rt

T = d/r

r = 5/8ft

d = 2/5ft

r/d = (5/8) * (5/2)

T = 25/8 seconds.

[Anonymous No.8988725]

>>8988712
Oh SHIT I didn't realize they were in English! That was one of the schools I was looking at too, thank you. I guess I need to look closer next time.

[Anonymous No.8988770]

>>8988468
Anyone know the answer? Feeling stupid for not knowing.

[Anonymous No.8988772]

If I'm given a set containing a couple of vectors and a vector field, how can I know if the set spans the field? I have to be able to write any vector in the field as a linear combination of the vectors in the set, right? But how do I know if I can do that?

[Anonymous No.8988776]

>>8988772
>vector field
do you mean a vector space?

>But how do I know if I can do that?
prove it algebraically

i.e. if you're looking at R^2 and have the vectors (0,1) and (1,0) then any vector (v,w) can be written (v,w)=v(1,0)+w(0,1)

[Anonymous No.8988795]

>>8988776
The problem I'm working on says to prove that S = {(7,0,3), (8,-4,1)} is not a basis for R^3. I tried: (0,0,0) = a(7,0,3) + b(8,-4,1), but I only got the trivial solution (a = b = 0), which means that the set is linearly independent. The solution manual, however, says that the set is linearly dependent, but does not span R^3. I don't understand why it says the set is linearly dependent.
I also don't really understand how they determined that it did not span R^3. They gave the example (0,1,0) cannot be written as a linear combination of the vectors in the set, but how did they get that vector? Did they just pick one at random and check?

[Anonymous No.8988799]

Just gave my periodic table quiz a play-through.

Let's see how I did, shall we?

[Anonymous No.8988808]

>>8988795
>I don't understand why it says the set is linearly dependent.
solution manual is wrong

>They gave the example (0,1,0) cannot be written as a linear combination of the vectors in the set, but how did they get that vector?
one way that works in this case is to use the cross product if you happen to know it since the cross product of two linearly independent vectors in R^3 gives a new vector which is linearly independent, otherwise you can just do it by inspection. (0,1,0) happens to work since
(0,1,0)=a(7,0,3) + b(8,-4,1) = (7a+8b,-4b,3a+b)
would require 7a+8b=0 and 3a+b=0 which is only possible with a=b=0, but then -4b doesn't equal the middle coordinate 1. so other choices that follow this reasoning is any non-zero vector of the form (0,c,0), but there are (infinitely) many other choices of vectors you could use

[Anonymous No.8988821]

I correctly named and placed all elements with the following exceptions:

I transposed the three pairs: Rubidium/Strontium, Hafnium/Tantalum, and Copernicium/Roentgenium. I correctly gave the symbols for all of the above except Copernicium (Cn), again just the transposition. No credit.

I also goofed the spelling of Platinum by adding an extra i, a la the British spelling for Aluminium. No credit.

I correctly identified the rows (periods) and columns (groups) of the table by same names, I just didn't pluralize them like I had it in my key. +2 credit.

Among types of elements, I incorreclty referred to polyatomic and diatomic nonmetals as being "ions". I did correclty identify post-transition metals there was just a spelling flub relative to my key, again. +1 credit.

Otherwise I goofed the symbols for Seaborgium and Antimony (transposing these two), Darmstadtium, Tennessine (Ts), Protactinium, and Thulium. No credit.

[Anonymous No.8988832]

>>8986488
Petrochemical Engineering

[Anonymous No.8988851]

Is race/ethnicity found in DNA? For example, I am mixed race but pass as white. If someone were to sample my DNA, could they tell my race?

I'm confused because many sources say race is largely not scientific, but some sources say they can tell your ethnicity/ancestors through DNA. Isn't that the same sort of thing?

[Anonymous No.8988861]

Why is bird poop white?

[Anonymous No.8988923]

>>8988861
Chickens isn't white.

[Anonymous No.8988958]

Why do we use the formula for the surface area of a cone frustum in deriving the formula for surface of revolution instead of using the surface area of a cylinder "2*pi*f(x)*dx" instead of "2*pi*f(x)*ds"?

[Anonymous No.8989223]

>>8987239
Steel wool acted as a heat sink

[Anonymous No.8989225]

This is a "lies told to children" tier simplification of time dilation, isn't it?

[Anonymous No.8989242]

how the fuck is this true? when rationalizing the numerator or separating it down to individual components via the properties of limits i can never find a way to make this equal -12/13. what retardedly simple and obvious solution am i not seeing?

[Anonymous No.8989253]

>>8989242

You can simply use l'hopitl rule and see it

[Anonymous No.8989257]

>>8989253
guess i'm working ahead because we haven't been taught that yet. thanks

[Anonymous No.8989280]

Trump unveiled a plan for a SOLAR WALL for his border wall plans. The solar wall will be solar panels. How viable of an idea is this really and how beneficial can it be?

[Anonymous No.8989294]

Is biology a waste of time? Opinion on Math?

[Anonymous No.8989311]

Is kinematics worth studying?, can we really ignore energy, torques and forces for something meaningful

[Anonymous No.8989508]

Is this a good linear algebra book?

[Anonymous No.8989524]

Suppose that I have a room that I want to heat up from 5 PM to 7 AM during the Australian winter, which has outside temps of roughly 5 to 18 C; how would I go about keeping a 40 cubic metre room at around 23 C, using renewable energy?

Could a solar water heater with a reasonably large insulated storage tank do the job, provided I could set up a suitable radiator?

[Anonymous No.8989536]

i heard that light is just photons, but it's also just electromagnetic waves of a frequency that happens to be in the visible spectrum. does this mean photons have an associated frequency? are x-waves, wifi waves any other electromagnetic waves also photons?

[Anonymous No.8989537]

Can someone explain the equivalence of the well-ordering principle and induction?

According to the wikipedia page on the peano axioms, the principle of induction is introduced to establish that every number succeeds some other number. However, on the page on mathematical induction, the equivalence proof uses that "every natural number is either zero, or n + 1 for some natural number n". But wasn't this a consequence of the induction axiom? Am I missing something or is wikipedia wrong?

[Anonymous No.8989551]

>>8989242
dont use l'hopitals unless you want to look like a brainlet. use [eqn] \frac{\sqrt{x^2+25}-\sqrt{13^2}}{x+12}=\frac{x-12}{\sqrt{x^2+25}+13} [/eqn]

[Anonymous No.8989663]

>>8989536
X-rays, and yes

[Anonymous No.8989678]

>>8989551
How

[Anonymous No.8989685]

>>8989678
because [eqn]\sqrt{a}-\sqrt{b}=\frac{a-b}{\sqrt{a}+\sqrt{b}}[/eqn]
for real [math]a,b\geq0[/math].

[Anonymous No.8989695]

>>8989663
wifi waves are photons? how come they go through walls? how come photons can go through a faraday cage, but not wifi?

[Anonymous No.8989713]

>>8989551
>dont use l'hopitals unless you want to look like a brainlet

How is using l'Hopital's anything other than a quick and elegant way of solving that limit?

Your mucking around with all that extra algebra is a total waste of time once you know about l'Hoptal's. Avoiding that kind of extra algebra is literally the whole point of why l'Hopital's even exists.

[Anonymous No.8989746]

>>8989685
>a=0, b=0 works

[Anonymous No.8989758]

>>8989746
i meant a,b>0 obviously

[Anonymous No.8989767]

Are proofs of trig identities necessary for higher math like calc and linear algebra. I find them so stupid, pointless and frustrating. It's so hit and miss and just consists of desperately trying to simplify and use other identities to get an identical expression. I'm thinking of just skipping the rest of the chapter because it's pissing me off

[Anonymous No.8989770]

Potato nigger dublin 4 faggot detected

[Anonymous No.8989778]

>>8989767
Give an example of a proof you consider pointless, and tell me what your goals are. Do you plan to get into engineering or into pure math or anything else?

Calculus and Linear algebra aren't really considered higher math, by the way. They're the very basics once you get to university.

[Anonymous No.8989789]

How does fusion work?

[Anonymous No.8989802]

>>8987338
As another example, old mine lanterns had their air vents covered by a metal mesh so they wouldn't trigger an explosion if there was flammable gases in the air.

[Anonymous No.8989816]

>>8989778
I just finished school so I meant higher as in college freshman level. I'm starting physics and chem next year. Any of these I consider pointless

[Anonymous No.8989861]

>>8988468
>difference of squares and factorization
completely unnecesary

Dividing by a fraction is equivalent to multiplying by its reciprocal.

[math]\frac{4x^2u-25u}{4x-10}*\frac{8}{2x+5}[/math]

Multiply across, pulling out [math]8u[/math] from the numerator

[math]\frac{8u(4x^2-25)}{8x^2+20x-20x-50}[/math]

Simplify and pull out a factor of 2 from the denominator

[math]\frac{8u(4x^2-25)}{2(4x^2-25)}[/math]

The [math](4x^2-25)[/math] terms cancel, leaving

[math]\frac{8u}{2}[/math]

which simplifies to [math]4u[/math]

[Anonymous No.8989864]

IS FIRE PLASMA? Like, the actual flame part.. that is plasma right?

[Anonymous No.8989866]

If fossil fuels are just crushed plants, why are we scared of an oil shortage/why are we investing in renewable energy? We should be able to synthesize crude oil in a lab.

[Anonymous No.8989873]

Can someone explain how he went from n=2 to n=1 in the term in red?

Here's the link for the whole solution: http://www.slader.com/textbook/9780538497817-stewart-calculus-7th-edition/1192/exercises/7/

[Anonymous No.8989876]

>>8989695
wifi is radio waves with a frequency of 2.4 Ghz, corresponding with a wavelength of about 12.5cm, too large to go through the nonconductive holes.

Visible light photons have a wavelength between about 300nm to 700nm, which easily fits through the bars in a faraday cage.

[Anonymous No.8989883]

>>8989864
Isn't is just glowing gas and/or soot?

[Anonymous No.8989892]

>>8989873
if n=1 then n-1=0 so n(n-1)c_n x^(n-1) =0 so the term doesn't add anything to the sum

[Anonymous No.8989893]

>>8989864
Not really. Most of a flame is incandescent soot. The cleanest fuels that don't make soot hardly have any flame; see hydrogen and especially methanol fires which are notorious for having invisible flames.

https://www.youtube.com/watch?v=RwmfBp3U2Os

[Anonymous No.8989901]

>>8989892
Oh, I see. Thanks.

[Anonymous No.8989903]

>>8989866
It is very easy to make oil in a lab, it just takes a lot of energy to do so. Oil made that way is only a store of energy, not the ultimate source of energy. Oil already formed in the ground takes a relatively small amount of energy to extract and refine compared to the energy required to synthesize it.

[Anonymous No.8989906]

>>8989294
>Is biology a waste of time?
From what I understand, Biology is one of the most respectable and hard sciences there are. Like, equal to or even greater than physics. Many of the greatest statisticians were biologists (e.g. Fisher).
t. math undergrad

[Anonymous No.8989916]

>>8989767
>Are proofs of trig identities necessary for higher math like calc and linear algebra.
lol no
Best way to remember them is through complex exponentiation.
For example:

cos(a+b)+isin(a+b) = exp( i(a+b) ) = exp(ia) exp(ib) =
= ( cos(a)+isin(a) ) ( cos(b)+isin(b) )
= [ cos(a) cos(b) - sin(a)sin(b) ] + i [ cos(a)sin(b) + sin(a)sin(b)]

and from this you get the identities for adition for both cosine and sine.
for the tangent you just write it out tan(a+b) = sin(a+b)/cos(a+b) = bla bla and you divide the denominator and the numerator by cos(a)cos(b).

[Anonymous No.8989948]

>>8989906
B-but maths i-isn't even a full science

[Anonymous No.8989962]

t. brainlet
I decided to get memed by /sci/ and swapped to spivak while 250 pages in another book, help w/ pic related notation, how would that product go and what's the meaning of f_i? is it a way to indicate the domain or what

[Anonymous No.8989965]

>>8989962
pic

[Anonymous No.8989970]

>>8989962
>how would that product go
well if i=3 and n=4 then it's
(x-x_1)(x-x_2)(x-x_4)

>what's the meaning of f_i
it's just a degree n-1 polynomial f_i(x) which satisfies f_i(x_i)=1 and f_i(x_j)=0 when j isn't i

https://en.wikipedia.org/wiki/Lagrange_polynomial
might be useful

[Anonymous No.8989979]

>>8986316
Hi /sci

How do I learn how to understand fancy formulas like pic related?

Can you recommend a single book or website where I could get started on the basics? I like reading sciency stuff but always get stuck on those mysterious scribbles.

[Anonymous No.8989981]

>>8989979
which part do you not understand, just the symbols?

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

[Anonymous No.8989994]

>>8989979
fastest way is :
https://en.wikipedia.org/wiki/Greek_letters_used_in_mathematics,_science,_and_engineering

Identify letter in the table, ctrl+f it and look for the usage that makes more sense given the context you found it in.
And what >>8989981 linked too if it's not greek alphabet

[Anonymous No.8990019]

>>8989981
>>8989994

What would lambda mean in the third formula?

[Anonymous No.8990129]

>>8990019
It's just a parameter (like how x is often used)

Lambda is often used for poisson distributions, this one looks kinda similar

[Anonymous No.8990155]

>>8989970
thanks, that was very helpful; analysis looks so much more interesting than calc, can't wait to get there.

[Anonymous No.8990187]

>>8986316
If nuclear fusion is brought about by the mass defect of smaller atoms achieving a higher packing fraction, then what perpetrates a Helium 4 nuclear charge from an alpha particle?

[Anonymous No.8990204]

>>8989789
it works by smaller atoms fitting together better with greater atomic weight- from a deuteron (proton and neutron) to helium 4, something like .6 of the percent mass is transferred into energy.

its more efficient than fission because of the mass to energy ratio; fission would have .3 instead of .6

[Anonymous No.8990260]

How difficult is it to acquire research assistantships and fellowships to get through a masters for free?

[Anonymous No.8990262]

>>8990260
what country?

[Anonymous No.8990266]

>>8990262
USA, EE and top gpa, gre, and two years relevant research

[Anonymous No.8990353]

I asked a question here and not getting responses, so I guess it was a stupid question
>>8990186

[Anonymous No.8990367]

>>8987954
depends on your prof, but mostly yeah.

>>8987947
study harder

>>8988001
/lit/

>>8988169
what a petty anon

>>8989225
that certainly is a lie

>>8989979
do you wanna know what they mean but you don't wanna learn the subject? you're not gonna get very smart off Wikipedia

[Anonymous No.8990501]

Will a masters make it easier or harder to get into a phd program? Assume masters is at much higher ranked school for same field of study (physics)

[Anonymous No.8990531]

>>8989713
8/10 bait. actually got a bit angry reading this

[Anonymous No.8990618]

why does everyone that matters support democrats

[Anonymous No.8990621]

>>8990618
but everyone matters anon. if you were a democrat you'd know that

[Anonymous No.8990622]

>>8990618
>why does everyone that matters support democrats
because if you don't you're a xenophobic racist sexist etc.

[Anonymous No.8990650]

>>8990618
It's better for business (for big businesses at least) to be world open, globalist and tolerant.
Do you think Sony would sell a lot of Playstations if they said "Japan first!!! Immigrants OUT!"
They would still sell well in Japan, but they're considering the international market too.
Businesses are not humans with emotions. They only care about money.
Actors (and other artistic people) are very similar. Unless you happen to be famous for some kind of racist role, you really don't want to turn large percentages of your audience against you.
Who knows what Robert Downey really thinks? He's still going to oppose Trump because he knows his movies are popular in Mexico.

[Anonymous No.8990708]

>>8990367
>do you wanna know what they mean but you don't wanna learn the subject?

I want to understand it just enough to be able to turn a formula into a computer algorithm.

I understand each symbol will have different meanings according to the subject but is there some basics common to all subjects that I could learn that would help me?

For exemple: Why does lambda have a funny hat in the 4th formula? What do I do with the 6 comparisons after the accolade in the third?

I think I have a good base in algebra, but would some statistics or calculus help me with the rest?

[Anonymous No.8990712]

I'm playing a game where you roll seven 10-sided dice. How do I find the probability of rolling seven different numbers?
Is it:
1 * 0.9 * 0.8 * 0.7 * 0.6 * 0.5 * 0.4 = 0.06048?

Or does (10 choose 7) appear in the calculation somewhere?

[Anonymous No.8990801]

>>8990712
0.06048 is correct.

10 choose 7 would apply only if you had some lottery where you draw 7 balls out of 10.

[Anonymous No.8990825]

>>8990367
So http://www.gregegan.net/ORTHOGONAL/00/PM.html is complete bunk? That's disappointing

[Anonymous No.8990886]

>>8990801
Thank you. How would I find the probability for certain combinations of numbers? For instance, with seven 10-sided dice, how would I find the probability of getting 3x of one number, 2x of a second number, and 1x each of a third and fourth?

Right now I have that as:
1 * 0.9 * 0.8 * 0.7 * (0.1*0.1) * (0.1) = 0.000504, which seems way too low.
That also seems to be equal to the probability of getting 4x of one number and 1x each of three other numbers, and that also doesn't sound right.

[Anonymous No.8990984]

If light, radio waves, X rays, etc are essentially the same thing (but of different wavelengths) does this mean radio waves etc are also made of photons?

[Anonymous No.8991065]

>>8990886
You're getting close. You have calculated for getting a triple, a pair and 2 singles in that particular order. Now you have to count the permutations.

7 dices can be ordered in 5040 arrangements. 7! (factorial). But permutations of the triple, the pair or the 2 singles are irrelevant so we divide them from the possibilities.

7! / (3! 2! 2!) = 210 unique permutations

0.000504 * 210 = 0.10584

[Anonymous No.8991067]

>>8990984
yes

[Anonymous No.8991073]

>>8991044

[Anonymous No.8991181]

>>8991065
Aha, the multinomial coefficient! That's what I was missing. Thanks a bunch anon.

[Anonymous No.8991322]

>>8991065
I'm a bit confused by something. Consider the case where you have 2 pairs and 3 singles.

Say you rolled 7 dice and got the result: 2, 2, 5, 5, 7, 8, 9. That's two pairs and three singles.

The probability of this would be the permutations times the chances of those results
I believe the chance of getting two pairs and three singles is
(1 * 0.1) * (0.9 * 0.1) * 0.8 * 0.7 * 0.6 = 0.003024
That is, your initial result, then the 0.1 chance of rolling that exact result again; then another number that's different from the initial result, and the 0.1 chance of getting that new result again; and finally the last three results are different from each other.

Would the number of permutations be 7! / (4! 3!) = 210,
or 7! / (2! 2! 3!) = 35 ?

The former would mean 210 * 0.003024 = 0.63504, which I know is wrong. It's much too high.
The latter would mean 35 * 0.003024 = 0.10584. I don't know if this is true or not.

If it is 7! / (2! 2! 3!) = 35, then I don't understand how the denominator terms are being decided upon. There are three singles, and those are combined into one term of 3!, to represent the permutations of those three individual numbers. There are two pairs, but those are kept separate?
There are 4! / (2! 2!) = 6 permutations of the two pairs. So would the number of permutations of the whole thing be 7! / (6 * 3!) = 140? Then 140 * 0.003024 = 0.42336, which still seems too high.

It's possible my "chance" result is incorrect too, but mainly, I've gotten lost about how to determine the denominators.

[Anonymous No.8991363]

>>8990618
Also, flooding immigrants into the country helps business lower wages as pajeet is just happy to be in America and doesnt care if his wage is less than average, it is still better than homeland wage.

[Anonymous No.8991436]

>>8987298
Best answer, but the way he phrased it makes it sound like he wants to know which major lets him feel superior to the largest number of peasants.

[Anonymous No.8991437]

Brainlet here. How exactly are inverse trig functions calculated? For example, why does [math]arcsin(3/5) = 36.8699°[/math] ? What is the calculator doing to spit out that number? Is it approximation based on known values?

[Anonymous No.8991443]

>>8991437
There is a big lookup table programmed inside.
If you try to calculate the arcsin of a number not in the table then it will lineary interpolate with the known values around it.

[Anonymous No.8991444]

>>8991437
just taylor it I guess, same as for sin

[Anonymous No.8991485]

I didn't want to make a thread about this question and I'm not even sure it's sci or k

I remember one day I read about stealth bombers that would taxi on the runway
On the way before takeoff the plane would actually leak fuel on purpose

Is this true or am I retarded

If true, why the fuck would the plane leak fuel on porpoise?

[Anonymous No.8991487]

>>8991322
haha, this is getting tricky. And I like that.

By aiming to get 2 pairs, you need to account for the permutations of the pairs. Rolling (1 1 2 2) is equivalent to(2 2 1 1). (With a triple and a pair we didn't have that equivalence. A triple cannot replace a pair.) So I discard the permutation of the 1st pair(2!), I discard the permutation of the 2nd pair (2!), I discard the permutations of the 3 singles (3!) AND I must also discard the permutation of the 2 pairs (2!) which are interchangeable.

7! / (2! 2! 3! 2!) = 105
105 * 0.003024 = 0.31752

If I was to look for 3 pairs I'd get
1 * 0.1 * 0.9 * 0.1 * 0.8 * 0.1 * 0.7 = 0.000504

I discard de permutations of the 3 pairs individualy (2! 2! 2!) and I also discard the permutations of the 3 pairs with one another (3!)

7! / (2! 2! 2! 3! ) = 105 again

0.000504 * 105 = 0.05292

For 2 triples I'd get
1 * 0.1 * 0.1 * 0.9 * 0.1 * 0.1 * 0.8 = 0.000072
7! / (3! 3! 2!) = 70 (the last 2! for the permutation of the 3 triples)
0.000072 * 70 = 0.00504

A triple and 2 pairs
1 * 0.1 * 0.1 * 0.9 * 0.1 * 0.8 * 0.1 = 0.000072
7! / (3! 2! 2! 2!) = 105 (again one more 2! for switching the interchangeable pairs)
0.000072 * 105 = 0.00756

[Anonymous No.8991490]

is pressure involved in the water ''force''?

e.g.

when i strangle a hose, the area becomes smaller so the velocity of the fluid is faster. however, the pressure is lower or p0 when the stream is out of the hose.

why do I feel like the stream is ''stronger'' when I do this?

is it only because of reynolds momentum equation? and pressure has nothing to do with it when the stream is in contact with the atmosphere?

[Anonymous No.8991502]

>>8991322
>>8991487
Just to be sure, I brute forced all the possibilities and they add up to the 10 million possibilities.

[Anonymous No.8991527]

>>8991485
You're thinking of the SR-71 Blackbird.

"Fuselage panels were manufactured to only loosely fit on the ground. Proper alignment was achieved as the airframe heated up and expanded several inches.[29] Because of this, and the lack of a fuel sealing system that could handle the airframe's expansion at extreme temperatures, the aircraft leaked JP-7 fuel on the ground prior to takeoff.[30]"

[Anonymous No.8991577]

What is typically covered in a course on linear algebra?
I've studied analytical geometry in high school, solving systems of linear equations and linear differential equations in undergrad, what else is left?

[Anonymous No.8991578]

Why can't i do this?

[Anonymous No.8991583]

>>8991577
Spectral decompositions of linear operators

[Anonymous No.8991681]

How long will our universe be habitable for?

[Anonymous No.8991797]

>>8986488
> PhD in theoretical physics, an immigrant from Ukraine became the most celebrated politician in modern history, delivering free quality healthcare, allowing gun carry, prohibiting the government agencies from spying on their citizens and introducing strict regulations on wall street, big oil, big pharma and jails as well as basically outlawing corporal lobbyism in America. He was the first POTUS to serve four terms and this PhD will have been me.
You now have the opportunity to tell me your concerns and desires.

[Anonymous No.8991853]

What's the best place to test your DNA to check ethnicity but more importantly health shit?

Looked at AncestryDNA, but they seemed obsessed with ethnicity.

[Anonymous No.8991920]

>>8988219
cuz I said so

but more seriously, I haven't read them, they're only on my list, but they're associated with a skeptical approach that can be useful when considering things like error in statistical models, future projections of the climate, etc etc

[Anonymous No.8991928]

>>8991920
>recommending authors you've never read
so this is the brainpower of /sci/...

[Anonymous No.8991963]

>>8990621
But some people matter more than others :^)

[Anonymous No.8992085]

Does anyone have a pdf of "Fox, J.E.D., 2000. Sandalwood: the royal tree. Biologist, 47:31"? My school doesn't give me access and I'm too dumb to find it otherwise.

[Anonymous No.8992450]

>>8986316
Ok so we've got our serotonin here
obviously

3-(2-Aminoethyl)-1H-indol-5-ol
But am i too stupid to see that the 3-(2-Aminoethyl) isn't where it should be? or how the hell do i rotate the molecule so that that 2-Aminoethyl group is at the 3? Can't for the life of me figure it out.

[Anonymous No.8992453]

>>8992450
Here's a solution I came up with, wouldn't that count as a chiral molecule though? or does rotation in 3D space count towards it not being a chiral molecule?

[Anonymous No.8992474]

>>8991487
>>8991502
You've been very helpful, thank you very much! Now I believe I understand it.

[Anonymous No.8992624]

Anybody has any good textbook about Calculus of variations? The more applied the better.

[Anonymous No.8992627]

>>8992624
>The more applied the better.
Just buy a mechanics textbook then.

[Anonymous No.8992697]

>>8992624
Also a very introductory text in optimal control theory would be nice too. The ones I found are very theory heavy and I only know up to PDEs using fourier.

>>8992627
Do you have one you recommend that covers variation? The problems I am interested in are also not just purely mechanical in nature, but that is a big part, I guess.

[Anonymous No.8992839]

Scientifically speaking, what's the optimal combination of pizza toppings?

[Anonymous No.8992881]

Was induction really necesary here or he is using it just to show me?

[Anonymous No.8992886]

>>8992881
>zero (0)
>natural number

[Anonymous No.8992904]

>>8992886
Whether to include the neutral element in the set of natural numbers or not is completely voluntary. To be painfully correct though you should subscript 0 to a squiggly italic N.

[Anonymous No.8992940]

>>8992886
>>8992904
That still doesn't answer my question guys

[Anonymous No.8992945]

>>8992881
>Was induction really necesary here or he is using it just to show me?

Depends. How is it defining the order?

If you define [math]a < b \iff \exists c \in \mathbb{N^*} : b = a +c [/math]

Then you can prove transitivity like this:
Suppose k < m and m < n. Then m = k + v and n = m + c. Therefore n = (k+v) + c = k+(v+c) and thus k < n.

HOLY SHIT.

HOLY FUCK MAN. I JUST REALIZED.

My proof is assuming that the + operation is associative. I JUST USED IT. But the proof in your pic does not use associativity. Holy fuck.

I take back everything before. Your proof is stronger as it does not use associativity. SHEEEIIIIIIIIIIIIIIIIIIIIIT. I'VE BEEN BAMBOOZLED.

[Anonymous No.8992972]

I am 1,000,000 years old and just had my first son. How old is my son going to be when he's exactly half my age?

[Anonymous No.8992978]

>>8992972
Come on man. This is pathetic. Literally just set up the equation and solve.

[Anonymous No.8992997]

>>8992945
The order is defined as m<n if m is an element of n. Is a set theoretic construction

[Anonymous No.8992998]

>>8990501

Easier if you have good grades and publish a good thesis or several

Harder if you don't

[Anonymous No.8993004]

What fucking book should I study before Baby Rudin?

I just finished a proofs course so I can write some proofs and I know some set theory, as well as finished a calculus sequence that used Stewart and then marsden/tromba.

I don't feel ready for baby Rudin and I have the whole summer. Someone told me Spivak, others told me to just find a simple intro to real analysis book and I even heard to skip all that and just learn topology

[Anonymous No.8993030]

>>8993004
If you know calculus and can read a basic proof you're fine to start analysis. Rereading calculus is largely a waste of time for you.
I think the best course of action for handling babby analysis is to do this; get Rudin and get another book (I used and liked Zorich, but there are literally dozens of good analysis texts that cover mostly the same shit). Don't read anything from Rudin; read your other book, and do all the problems out of Rudin.
Rudin has awful writing, especially for inexperienced undergrads, but 10/10 problem sets.

[Anonymous No.8993040]

>>8988209
bump-o-runi

[Anonymous No.8993045]

>>8991928
Hey, you asked and I offered help. At minimum, it can give you good leads, and so quickly judging one's brainpower off such only inidicates your own lack of it, so I'm ready to hear your apology now.

[Anonymous No.8993086]

>>8992839
80% sausage
20% pepperoni
0% pineapple
The science is settled

[Anonymous No.8993138]

>>8990266
RA's go to doctoral students. It's very uncommon that master student's get an RA. But, you do sound qualified.

[Anonymous No.8993194]

When reading this, I need to do something. Look at the farthest object relative to your current position. Put your finger up to your eye while look at it, and move it very slightly. From where you stand your finger has moved maybe a centimeter, but if you did this while looking at the night sky, you have moved across billions and billions of miles. With this in mind, I present you my question

Say while exploring space with your telescope, you moved it in the tiniest fraction of a distance physically possible. Would it move too much for you to see the what was in between the two points you've moved from your telescope to that region of space you were exploring or can we not see that far yet for it to be possible, but when and if possible, is there a solution to this?

[Anonymous No.8993291]

For the hell of it, because science, can we strap dolphins in spacesuits and launch them into orbit? The suit could filter and spray water on their skin, and a pipe send oxygen to their blowhole.

[Anonymous No.8993409]

Do (white) American men have bigger dicks than Europeans?
This is anecdotal, but most men I know (I'm German) tend to have an average dick size of 5-6 inches, while with American men I always hear they have huge monster dicks that are 7-8 inches or more. I hear this from men bragging about their dicks online, but also from girls who have dated American men.
Of course the national average gets dragged down because America has a lot of ethnic diversity, so i'm talking specifically about white men.

[Anonymous No.8993417]

>>8992450
>>8992453
no one answered so self bump for this SQ

[Anonymous No.8993428]

>>8992881
Obviously you could just use the transitivity of "<" on N to prove it, if you like circular reasoning

[Anonymous No.8993440]

>>8993409
USA has an average of 5.0
Germany has an average of 5.6
Black countries usually have averages higher than that

No, americans do not have a larger penis then Europeans.

[Anonymous No.8993458]

>>8993440
Yeah but there aren't even that many blacks in the US, compared to Hispanics. They're the ones to pull down the average, I assume.

[Anonymous No.8993485]

>>8993458
let's, for sake of simplicity, all hispanics in the US are mexican
mexican average size is 5,94 inches (mind you lmao this is higher than the average US size)
and there are 35 million mexican americans
that would mean that the average White americuck has an even smaller penis than the national average
http://klaq.com/worldwide-penis-survey-heres-the-chart-were-talking-about-this-a-m/
https://en.wikipedia.org/wiki/Mexican_Americans

So, yeah your assumptions need to be reversed .

[Anonymous No.8993501]

>>8993485
That's actually hilarious.
Then how can it be that all these women told me their American partners had 7 and 8 inch cocks?

[Anonymous No.8993505]

>>8993501
Really no clue. Maybe because that's what their partner told them? Even though they might just be 5-6 inches. people overestimate their penis size a lot, and the partners just believe it.
anyways, Americans are hilariously under-average.

[Anonymous No.8993524]

>>8992972
the same age as you are now

[Anonymous No.8993935]

What's the difference between a real-valued root and a principal root?

[Anonymous No.8994025]

>>8989551
You've made a mistake though. It's
[math]x^2 - 12^2 \over {(\sqrt{x^2+25} + 13) \times(x+12)}[/math]
Should have used L'hopital

[Anonymous No.8994060]

Can someone explain how cosmological horizons are supposed to work? Beyond the Wikipedia entry.

If no objects can travel faster than light, then any light which is directed such that it will meet with any object will eventually meet with that object given a sufficient amount of time.

I heard the brainlet Laurence Krauss say that space can expand such that the distance between two regions of space is too great to be crossed in a finite amount of time by any light, but why suppose that space will expand in the between-region of space at a rate which is constantly greater than the speed of light?

[Anonymous No.8994064]

>>8994025
[math] x^2 - 12^2 = (x+12)(x-12) [/math]

[Anonymous No.8994065]

Is negative mass just a mathematical toy, or can it exist?

[Anonymous No.8994097]

>>8986316
Stupid questions do not exist, but inquisitive idiots do.

[Anonymous No.8994114]

>>8994025
look! a stray cross product

[Anonymous No.8994117]

>>8994025
l'hopitals confirmed the brainlets choice

[Anonymous No.8994131]

Which is the best book if I want to study limits? I'm struggling with some pretty difficult ones.

[Anonymous No.8994133]

What is the maximum energy density of graphene boron nitride mim nano capacitors? Wh/kg? The papers I read don't list this number. I mean if eldc capacitors get their energy density from accessing the surface area more easily, then these nano capacitors should have just as much energy right.

[Anonymous No.8994137]

I haven't done math in years and only remember basic algebra. Will completing I.M Gelfand's books (Algebra, Functions and Graphs, Method of Coordinates, Trigonometry) give me a stable foundation to work upon?

[Anonymous No.8994171]

>>8990708
>is there some basics common to all subjects that I could learn that would help me?
Subscripts and the capital sigma are pretty universal.

>Why does lambda have a funny hat
Because lambda without a funny hat is already used.

>What do I do with the 6 comparisons after the accolade in the third?
Insert "if" after the comma in each line, and remember what you learned in middle school calculus.

[Anonymous No.8994195]

>>8988468
it's a difficult problem

[Anonymous No.8994205]

>>8994114
Skalars are just vectors of size 1

[Anonymous No.8994210]

>>8994205
>size 1

[Anonymous No.8994226]

If you starve to death do you still shit yourself?

[Anonymous No.8994247]

>>8994205
stop

[Anonymous No.8994251]

>>8994226
1. Not everyone shits themselves when they die, only if they have been holding.
2. You have diarrhea and clean up your exhaust before you die of hunger.

Also I think the most common way to starve to death is to shit yourself repeatedly due to some bacteria or body condition.
So you die from shitting yourself, instead of shitting yourself upon death.

[Anonymous No.8994253]

>>8994251
>shit yourself repeatedly due to some bacteria or body condition
kills you by dehydration, see dysentery

[Anonymous No.8994264]

>>8994253
In medieval Africa, maybe. Today you get plenty of water, just have trouble getting food in, so you lose weight fast, starve, and even with food being poured directly into your blood eventually die from malnutrition.

Its how you starve in 21st century modern life, by shitting yourself for three months.

[Anonymous No.8994307]

Mathlet here what kind of basic tutorials should I read to understand how to translate coordinates in which the top left of the screen is (0, 0) to graph? Like I want to graph stuff but the window coordinates starting at the top left how do I translate graph coordinates into window coordinates so I can draw the graph on the window?

[Anonymous No.8994308]

Can anyone with a simulator tell me how close planets can be without fucking things up? Is my dream of a planetary neighborhood of several earth-like planets close together just a meme?

[Anonymous No.8994323]

I need help with a problem. I just need some tips on how to approach it because I'm lost.

Let [math]G[/math] be a finite group of order n. And suppose that for every divisor [math]d[/math] or [math]n[/math], there exist at most [math]d[/math] elements of [math]G[/math] that satisfy [math]x^d = 1 [/math]. Prove that G is cyclic.

[Anonymous No.8994327]

>>8994323
*for every divisor d OF n

[Anonymous No.8994330]

>>8994264
wow

[Anonymous No.8994331]

>>8994307
y = height-y

[Anonymous No.8994337]

>>8994331
But I'm trying to look over some tutorials and they are using all this complicated stuff like matrices and stuff. Are they complicating it or is all that really necessary?

[Anonymous No.8994340]

>>8994323
>>8994327

[Anonymous No.8994353]

>>8994337
Matrices are for complicated transformations such as rotations. But if you just want x-scaling and y-scaling, you can write it as a diagonal matrix.

Maybe you want something like
drawX=(x-xmin)/(xmax-xmin) * windowWidth
drawY=windowHeight - (y-ymin)/(ymax-ymin) * windowHeight
//assuming the aspect ratio is correct

[Anonymous No.8994366]

>>8994340
What is the definition of "cyclic Group"?

[Anonymous No.8994370]

>>8986316
Trying to understand Church Numerals.
In pic related, they define zero as essentially
[math]0 \equiv \lambda f. \lambda x. x [/math]
Which I take to mean that for any function f and input x, if you apply zero( f(x) ) you get x as an output

I'm assuming that they define "(add-1 n)", where n is an input function, as

[math]\lambda n. \lambda f. \lambda x.
(f ((n f) x) )
[/math]

If you apply "zero" to the above "add-1" definition you (maybe?) get the following:
[math]
\lambda n. \lambda f. \lambda x. (f (( \lambda f. \lambda x. f) x))
[/math]

My question is, does this reduce to:
[math]
\lambda n. \lambda f. \lambda x. (f (x)
[/math]
If so, how?

[Anonymous No.8994372]

>>8994131
Sup /sci/

[Anonymous No.8994378]

>>8994366
A group that is generated by a single element.

[Anonymous No.8994447]

>>8994370
Let's write \x->e for [math] \lambda x.\,e [/math], so I don't have the do math tags. Btw. that's Haskell notation, pic related.*

>Which I take to mean that for any function f and input x, if you apply zero( f(x) ) you get x as an output
>if you apply zero( f(x) )
You may pass any f to zero, and what you get is \x->x. This is the identify function.
Note how in this particular function, f is ignored and whatever you pass zero as first argument, you always get the identity function.

>If you apply "zero" to the above "add-1" definition
you apply "add-1" to "zero". But okay, details.

Your next line seems to be wrong. If n is zero, then n f is the identity function.
If you plug in the identity function, then the next step is that (\x->x) x reduces to x and you're done.

*btw. I just started a youtube channel where I'll go thought the basics of the dependently typed programming language Idris

https://www.youtube.com/channel/UCcrSMnEYhIPX_p127jI23qw/playlists

[Anonymous No.8994449]

I want to learn how to use CRISPR to engineer plants and mice.

Where do I start if I minored in biology?

[Anonymous No.8994455]

>>8994447
Thanks!

Best of luck with your YT Channel.

[Anonymous No.8994487]

For all you biologists out there:

Could life find a way inside a nebula? I've heard of alcohol and organic matter being found out in deep space. Is it possible for an ecosystem to develop in a vacuum?

[Anonymous No.8994506]

>>8994378
What does it mean for a group to be "generated" and what is a generator?

[Anonymous No.8994516]

>>8994449
you should browse the faculty webpages of your local institutions for labs that perform CRISPR and inquire about/apply for a research technician position. the alternative is, if your major is something like chemistry, you could apply for graduate school, where you will go through lab rotations and can choose a dissertation lab that uses CRISPR.

>>8994487
i strongly doubt it. if it were true, then that form of life would not be anything like biological life as we know it. i suppose anything is possible however

[Anonymous No.8994541]

>>8994353
It looks like the library I'm experimenting with actually does have something like this, is this what I'm looking for? But not sure how to use it because the documentation for this library is basically nonexistent and I had to grep through the source to find this.

[Anonymous No.8994585]

Can somebody explain why the absolute value of omega is negative for omega less than zero? Losing my fucking mind over this right now.

[Anonymous No.8994598]

>>8994585
https://en.wikipedia.org/wiki/Absolute_value#Definition_and_properties

[Anonymous No.8994609]

>>8994585
the absolute value of -3 is -(-3) = 3

[Anonymous No.8994651]

Can I still move into industry after a postdoc or is it harder? For EE

[Anonymous No.8994890]

>>8994065
We don't know but we're pretty sure it's unlikely.

[Anonymous No.8994896]

>>8994598
>>8994609
Oh god damn it.
abs(x) = -x when x < 0 because that makes it positive.
Fuck.
I'd never seen this notation before it really threw me for a fucking loop.

[Anonymous No.8995034]

>>8988209
BUMP

[Anonymous No.8995165]

>>8994506
If S is a subset of a group G, then [S] is the subset of G which consists of all products of elements of S and their inverses. It is a subgroup which is called "the subgroup of G generated by S". It can happen that [S]=G. In that case, we say that G is generated by S, and its elements are called generators.
If there exists a finite subset S such that G=[S] then G is said to be finitely generated. If there exists an S with #S=1 such that G=[S], then G is said to be cyclic.

All cyclic groups are isomorphic to either Z or Z/nZ.

[Anonymous No.8995169]

>>8994506
>>8995165
There can be many different generating sets. Here >>8994340 Jean-Pierre takes all the elements x such that {x} is a generating set for C_d, and puts them all in a set, which he calls Φ_d.
But if this is new for you, you might want to read an easier book on arithmetic first.

[Anonymous No.8995461]

Say I have a list of values [math] x_1, x_2, x_3, ..., x_n [/math]
And i am supposed to find the "expected value" for any [math] x_i [/math].
How would I do it? Take the median or something?

[Anonymous No.8995465]

>>8995461
>I have a list of values x1,x2,x3,...,xn
Are they from independent and identically distributed random variables X1, ... Xn?

> am supposed to find the "expected value" for any xi
I don't understand what you mean by that

[Anonymous No.8995662]

>>8995461
[eqn]E(x) = \frac 1 n \cdot \sum_{i=1}^n x_i[/eqn]

[Anonymous No.8995670]

>>8995461
>>8995662
Maybe it should be an x hat instead of E(x)

[Anonymous No.8995703]

>>8995662

Expectation of a random variable is defined as the vector of elements in the domain of the distribution of the random variable, dot product(/inner product) with the probability at each element.

In your case, assuming a uniform distribution, each element has probability of 1/n, so the expectation is the sum of each realization multiplied by 1/n.

[Anonymous No.8995708]

>>8986316
Are there maglev bearings that would also be able to restrict a large amount of centripetal (or centrifugal, whatever you wish to call it) force?

I try drawing some ideas but they all look like weapons out of Half-life.

[Anonymous No.8995731]

>>8995662
That is the estimator of the expected value, not the actual expected value.

[Anonymous No.8995760]

>>8987239
I don't know the exact answer to your question bro but you might find it here somewhere: https://en.wikipedia.org/wiki/Safety_lamp
Using gauze/mesh to prevent flame ingress was a common concept used in miner's lamps

[Anonymous No.8995771]

>>8988050
Hobby chemist (for a long time) here
A burette and volumetric flask are of course indispensable if you're going to be doing quantitative work. If you're not immediately planning on doing that, skip those as they tend to be expensive.
At the very least you need some beakers, erlenmeyers and graduated cylinders to start out with, and of course test tubes. Thermometer is a no-brainer. I don't recommend buying jointed glassware as your first purchase, I took many years before advancing to that. But if you have the money and want to jump straight into it, don't buy a graham and single three-neck. You should rather get a basic distillation kit with a liebig which is more flexible.

Just don't use jam jars or shit like that and remember that kitchenware "Pyrex" is worthless trash.

[Anonymous No.8995826]

If I have a 20W engine (20*1.66) but the supply is 12V*2A is the engine gonna drain 1.66A only or is it gonna BURST INTO FLAMES ?

[Anonymous No.8995828]

>>8995826
12*1.66 obviously*

[Anonymous No.8996041]

I'm going to be a sophomore dual physics and math major next semester at university. Last semester I took:
- Complex Variables
- ODES
- Intro to Proofs class
- Quantum Mechanics
3.7 GPA
I know I am ahead compared to what is considered the normal track, but is it a plus when applying for internships and grad school? Is it considered normal for competitive students or what?

[Anonymous No.8996326]

>>8996041
Maybe internships if they require certain courses, but grad schools dont care how long you take to graduate as long as you do well and have research and good letters

[Anonymous No.8996339]

People say to not care as much about top grad schools and look more for top professors in your field, but how do you find this info? Do you just find professors with a lot of citations or something? Wont top ranked programs have top professors? Interested in optics/photonics if anyone can point me in the right direction

[Anonymous No.8996391]

>>8986316
If I am moving at a relativistic speed in a spaceship then my time would appear to run slower for an observer at rest, does this mean that everything I see in the universe around me happens faster?

[Anonymous No.8996561]

>>8996391
Well from your frame everything would be moving past your at that relativistic speed

[Anonymous No.8996617]

What do the holes in amber really contain?

[Anonymous No.8996620]

>>8996617
>What do the holes in amber really contain?
God.

[Anonymous No.8996627]

>>8996617
Prehistoric farts

[Anonymous No.8996628]

>>8996620
I mean, what happened to the inclusions?

[Anonymous No.8996649]

>>8996628
got trapped

[Anonymous No.8996658]

How much of pre history do we know? Suppose there was an iron age yet completely coastal civilization some 13,000 years ago? Is it even remotely possible that with the sea level rising after the Ice Age we could find no remains today of said civlization?

[Anonymous No.8996782]

Hello,

I am such a huge brainlet, that despite studying satisfactorily, I can never reach good results academically, and I now think it's related to problems down to biological level, not simply psychological.
(I'm currently on a Computer Science course, by the way)

Ever since high school I have been facing these problems, bombing hard on some exams despite putting more effort in comparison with some "normal/non-geniuses" classmates.
I even made a thread on /adv/ asking about the same question before but got no replies as that place is populated by Chads with womyn problems.

I have been previously diagnosed with bad functioning Short-term memory before, along with some (minor) anxiety problems.

What kind of mental gymnastics, drugs and diet can I take to improve my cognitive skills?

I'm 24 btw (too old to try a lengthy therapy, also delaying my graduation because I'm failing many courses)

[Anonymous No.8996947]

What are the career differences between majoring in statistics, and being a pure math major taking statistic electives?

[Anonymous No.8997047]

>>8996782
Look into Carl Newport's blog Study Hacks, particularly his articles on studying for tests, productivity, and active recall. I used to be like this but taking his advice helped me a lot.

[Anonymous No.8997049]

What moves the axles of a car? Is it the camshaft, crankshaft, or pistons

[Anonymous No.8997368]

>>8994308
The wiki page on the Roche limit has some nice equations to fuck around with.

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

[Anonymous No.8997379]

>>8995708
Normally you would just bank the track so that at the design speed the sum of the weight and the cent*****al force is normal to the track.

[Anonymous No.8997396]

Here goes, guys:
we take the metal out of an old mattress
we connect it straight to the standard high voltage line

what's the energy intake?

[Anonymous No.8997398]

>>8995826
>>8995828

The motor is only going to draw what current it needs to achieve the voltage drop of 12V. It would need a higher voltage than what the power supply can achieve to draw 2A.

From ohms law, the resistance of the motor is 12/1.66=7.23ohm

7.23ohm*2A=14.46V required to draw 2A

The power rating on motors is pretty flexible anyway.

[Anonymous No.8997403]

>>8996658
You mean like Doggerland?

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

[Anonymous No.8997415]

>>8997049
Spider carrier in the differential.

>camshaft, crankshaft, or pistons
crankshaft and pistons yes, camshaft no

Path of power from combustion to axles:
piston->crankshaft->flywheel->clutch/torque converter->transmission->(driveshaft if RWD)->differential->axles

the camshaft only drives the valves in the engine

[Anonymous No.8997429]

>>8994487
>https://en.wikipedia.org/wiki/Doggerland
my friend once pointed it out for me, that there might be life on the sun and we would never know.

of course it would be really different from us, happening in a different time frame and using strange chemical processes

I guess the vacuum itself isn't a problem, as even our bacteria can survive it.

[Anonymous No.8997441]

>>8997429
oops, that link has nothing to do with anything. just a typo

[Anonymous No.8997466]

>>8997047
Ok, thanks anon...

I made a quick retrieval for those who are interested:


http://calnewport.com/blog/2009/03/09/the-straight-a-method-how-to-ace-college-courses/
http://calnewport.com/blog/2008/07/03/case-study-why-the-number-of-hours-you-spend-studying-means-nothing/
http://calnewport.com/blog/2008/04/28/monday-master-class-the-study-hacks-guide-to-exams/
http://calnewport.com/blog/2008/04/29/my-world-famous-mechanical-exam-prep-process/
http://calnewport.com/blog/2008/02/15/fixed-schedule-productivity-how-i-accomplish-a-large-amount-of-work-in-a-small-number-of-work-hours/
http://calnewport.com/blog/2017/01/05/on-rooted-productivity/
http://calnewport.com/blog/2012/08/10/you-know-what-you-write-the-textbook-method-for-ultra-learning/
http://calnewport.com/blog/2007/10/03/the-art-of-stealth-studying-how-to-earn-a-40-with-only-10-hours-of-work/

[Anonymous No.8997475]

>>8986316
Is there a nice page to download scholar papers for free? I found the stuff I'm looking for in philpapers.org, but it redirects to other pages where I have to pay but I'm poor and I'm not willing to waste money to write a shitty report.

[Anonymous No.8997478]

>>8997475
>>8997475
>Is there a nice page to download scholar papers for free?
http://sci-hub.bz/

[Anonymous No.8997485]

>>8997478
Thanks anon, you saved my ass.

[Anonymous No.8997506]

I was reading and came across the summation for e...
(1 + 1/n)^n for n 1 -> inf

Now I know the system often used is the base 10 system where fractions are defined as "slices" out of ten, or numbers are counted in "tens places".

Is there such a system that is base e, so as e is not an approximation but made to be an exact number that other numbers build on?

[Anonymous No.8997514]

What is the point of dying?

[Anonymous No.8997515]

>>8997514
no point at all.
don't do it

[Anonymous No.8997523]

>>8996561
if I look at an outside clock it would appear to run faster, right?

[Anonymous No.8997709]

>>8997671

[Anonymous No.8997747]

>>8997523
Use the equation in pic related. You are the observer and everything around you would be moving at that relativistic speed and the moving clock would be outside your reference and you would have the rest frame

[Anonymous No.8997764]

in Electricity & Magnetism why is it that one can use The voltage induction law or the Wiener filter law interchangeable ? U ind = B*s*v U win = B*d*v
How would i show that these are essentially the same ?

[Anonymous No.8997801]

>>8997506
Yes, you can use practically any number as a base
For example, 234 in base e would be [math]2e^2 + 3e + 4 \approx 26.93296...[/math] in base 10
The actual intuitive meaning of an irrational number base, i'm not so sure on that

[Anonymous No.8997966]

>>8997396
bump

i know this question is weird, but I legitimately need to know the answer and I don't know shit about physics.

[Anonymous No.8998044]

>>8997514
To make room for others

[Anonymous No.8998047]

>>8996947
Bump

[Anonymous No.8998049]

>>8997396
Well, it needs more information.
How many volts is the High Voltage source?
How big is the mattress?

What is the purpose of the experiment?

[Anonymous No.8998080]

>>8998049
ok, so I've been told a story, that is supposed to actually have taken place:
>Hungary, some time ago
>a major town in the region decides it's time for some philanthropy
>they grant a gift to a little Gypsy village:
>they'll give them the electricity for free

I mean, how much energy can 40 houses use? especially if they don't have washing machines, hairdryers/computers/etc.

>for the first day and night everything goes smoothly
>second night
>suddenly the displays go crazy
>it seems that the village is sucking *enormous* amounts of energy
>two men are sent to investigate

>they enter village
>everything is dark
>everything is quiet
>no lightbulbs turned on, no tvs, no nothing
>they go further into thee village
>finally, they find one singe house with light inside
>music played loudly
>people dancing half naked
>they get inside
>in the center, they see:
>a metal part of the mattress
>connected to two cables from the high voltage line
>fucking glowing, giving out intense amounts of heat


So I would really like to know, if this is in any way possible to be actualy true

It's obvious it might burn the house, but lets assume that's not a problem for some reason.

I've no idea about the mattress size, so lets go with the standard (I'll try to google it in a moment)

the voltage should also be assumed to be the standard stuff going through the cables used to power the villages. I thought there is but one standard. Maybe any of you anons kow the numbers?

I would like to know how much energy could be sucked this way. And whether the metal would melt or not.Again, Idon't know what kind of metal is used, but I guess it's the cheapest iron.
You know, even if it could be dissmissed as bullshit from the very beggining, I'm really curious to see the 'what if'

[Anonymous No.8998094]

>>8998080
https://en.wikipedia.org/wiki/Bed_size#Table_of_common_sizes

so let's just assume that the size it's something between 20cmx70cmx170cm and 30cmx100cmx200cm

I have no goddamn idea how much metal might be contained inside, but since it's usually carryable by two people, who have to strain a lot, I'd assume something like 60 to 80kg

[Anonymous No.8998206]

How do I stop fearing for an universal phase transition? I'm spooked by the thought of disappearing in an instant with no warning.

I don't necessarily want rational arguments against my fear, just something that would avert my mind from this. Is our physical paradigm still decidedly incomplete and likely that phase transitions as they are currently formulated could not probably occur?

Any psychological exercises for forgetting this?

[Anonymous No.8998213]

>>8998206
dude, but this would be AWESOME

seriously, try to think about the cool things that might happen

[Anonymous No.8998217]

>>8998213
Fuck you anon I'm experiencing existential terror here

Not that I would be able to see the outcome of such a reaction

[Anonymous No.8998229]

>>8986316

if I plot careers on a graph where the x-axis measures flexibility, and the y-axis represents lifetime earnings, which careers would be on the top right?

[Anonymous No.8998234]

>>8998217
but dude, you're gonna die anyway
maybe just start enjoying life before it's too late. Iknow a lot of people whom this solution helped. No more fear, since you're doing your life right, so you're prepared to die at any moment

[Anonymous No.8998239]

>>8998234

I probably will know when I die if it is not from a transition

I cannot put the second half of your post in practice

[Anonymous No.8998271]

>>8986316

Is this course any good? Should I use it to learn linear algebra, or should I just use the /sci/ wiki's recommended book for L.A?
https://ocw.mit.edu/courses/mathematics/18-06sc-linear-algebra-fall-2011/

[Anonymous No.8998282]

>>8998271
/sci/ wiki is a meme, go with mit

[Anonymous No.8998349]

>>8998080
>>8998094
So basically, a giant heater / toaster without shielding.
Seems like at least a possibility to be true, given they short circuited the power supply.
Did you want a mathematical answer?

[Anonymous No.8998369]

>>8998349
since I never was into the field, I don't quite know what a mathematical answer includes.

I'd like to know the numbers and brackets on them. I probably won't understand the equations behind them anyway, so that's not really needed.
But I would really like to know what exactly would likely happen, how fast, what would folow. Especially, how much energy would it take, how much heat would be produced, what would happen to the metal. And would the energy loss be enough to be noticeable by the nearby town?

[Anonymous No.8998573]

>>8998206
You should look up other scary ideas, such as new age nonsense, philosophical thought experiments and conspiracy theories.
That way it's easier to see your particular worry as just one of the many bullshit ideas caused by incomplete information.

[Anonymous No.8999241]

>>8986316
If you throw a pencil away from you in space, do you accelerate as fast as the pencil?

[Anonymous No.8999246]

>>8999241
The pencil doesn't accelerate after it leaves your hand.

[Anonymous No.8999252]

>>8999246
Thanks, but I actually meant to say "speed". What about now?

[Anonymous No.8999255]

>>8999252
The conservation of momentum states that your velocity will change in the direction opposite you threw the pencil.

[Anonymous No.8999275]

>>8986609

[Anonymous No.8999288]

>>8999255
True, but will the pencil and the person move away from each other at the same speed then? I suppose mass doesn't affect anything here?

[Anonymous No.8999294]

>>8999288
The average human is 70 kg, and a small pencil is 1 gram. Since the human is 70,000 times as massive as the pencil, the pencil will be about 70,000 times faster than the human, because m1v1=-m2v2.

[Anonymous No.8999493]

>>8999294
Doesn't the aspect of things being weightless in space influence this though?

[Anonymous No.8999526]

>>8999493
No. Momentum depends upon mass, not weight.

[Anonymous No.8999527]

>>8999526
Thanks