/sqt/ - Stupid Question Thread: Tuesday Edition

How did they get the last expression?

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

seconded

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

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?

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.

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.

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

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

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}

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

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?

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

A cold?

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?

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)

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.

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

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.

Redpill me about philosophy, /sqt/.

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.

Nevermind, it's trivial

>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.

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

>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, Veeky Forumsentists?

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

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

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

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?

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.

>Russel, Popper, Khun and Heil
why?

Majoring in data science would be a decent starting point

Why is bird poop white?

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

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

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

describe the complementary graph...

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

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?

>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

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?

>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

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).

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?

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

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

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.

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?

how did you get 15/8

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

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

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

25 / 8 sec

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.

german's a dying language, just learn arabic instead

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

D = rt

T = d/r

r = 5/8ft

d = 2/5ft

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

T = 25/8 seconds.

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.

Anyone know the answer? Feeling stupid for not knowing.

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?

>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)

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?

Just gave my periodic table quiz a play-through.

Let's see how I did, shall we?

>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

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.

Petrochemical Engineering

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?

Why is bird poop white?

Chickens isn't white.

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"?

Steel wool acted as a heat sink

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

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?

You can simply use l'hopitl rule and see it

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

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?

Is biology a waste of time? Opinion on Math?

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

Is this a good linear algebra book?

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?

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?

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?

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]

X-rays, and yes

How

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

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

>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.

>a=0, b=0 works

i meant a,b>0 obviously

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

Potato nigger dublin 4 faggot detected

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.