/sqt/ smol question thread

[Anonymous No.10234461]

the questions in here are smol

[Anonymous No.10234471]

Copying last post from previous thread.

The problem is for larger systems (than 20 electrons), calculating the exact electron density (and getting the exact wave function in the first place) is impossible due to the binomial scaling of the Full Configuration Interaction (FCI).

For small systems however it is possible. I want to see if I can find a good expression for the functional that reproduces (or is sufficiently close, say 95%) to the exact ones and see, if the approximate method, which is linear scaling and super super fast, is also good for larger systems where a FCI calculation is impossible.

[Anonymous No.10234476]

>>10234461
Stop posting your anime shit. You are ruining the stupid question thread. This thread are for newfags who dont know what the fuck is sqt.

[Anonymous No.10234483]

>>10234476
Seething

[Anonymous No.10234504]

>>10234471
Is this right >>10234481 ?

[Anonymous No.10234543]

>>10234461
I liked smol the first time, but you don't need to make every one the smol question thread.
Call the next one "slippy questions thread" and attach Tsuyu.

[Anonymous No.10235337]

Why the fuck is math and science so boring? The big picture of any field isn't boring. But as soon as you delve into the details, it becomes a chore. I don't want to memorize 100,000 different words to learn medicine. I don't want to do a million tedious math problems to understand math. etc. etc. Is it just the way the universe is? Is it a fundamental flaw in the way humans think and learn and communicate? How do we fix this?

[Anonymous No.10235358]

>>10235337
>he doesn't know about economics
Just don't get into econometrics.

[Anonymous No.10235401]

>>10235337
It's a flaw in your thinking, actually. Without delving into the details you can't generate the big picture in the first place. You have the luxury of imagining otherwise because other people have tried to summarize the big picture for you.
You've never actually seen it, and it doesn't exist except as the totality of details you seem to despise.

[Anonymous No.10236934]

I am a brainlet. Please comment on my brainlet explanation of a powerset:
A powerset is a set that contains the many possible subsets of different sizes, including an empty set, that can be made from a source set S. If S has n elements, the powerset of S will contain 2^n subsets.
A source set of {1,2,3} will thus give {{}, {1}, {2}, {3}, {1, 2}, {1, 3}, {2, 3}, {1, 2, 3}}

[Anonymous No.10236943]

>>10236934
No idea why you don't just think of it as the set of all subsets, but sure, it works.

[Anonymous No.10236948]

>>10234461
How do you solve motherfuxking trig bullshit??? Take sin(x) + 3*cos(x) < √6 for example.
I know you're supposed to use trig identities of something to solve for x but I don't remember this high school nonsense.

[Anonymous No.10236957]

>>10236948
You'll usually use
[math]cos^2x+sin^2x=1[/math] to remove one and solve for one variable.
I think there's actually still some space where the sine is negative but that's still true, which is the annoying part of the solution;

[Anonymous No.10236977]

>>10236948
Didnt you literally just make a thread about this?

[Anonymous No.10236979]

why are two sines of the same frequency that are out phase only influence each other's loudness, but it's only when i shift the pitch of one of the sines the beating is heard?

[Anonymous No.10236987]

Is a 5 year degree equal to a Masters in the American education system?

[Anonymous No.10236996]

>>10236987
I doubt it. Depends on the curriculum or courses taken, but I still doubt it.

[Anonymous No.10237007]

>>10236979
If they're at the same frequency then the phase shift and the combined amplitude are constant. When one frequency is slightly off from the other, the waves slowly phase in and out of sync and the resulting amplitude oscillates.

Go to Desmos and graph
>sin(x)+sin(x+.01)
vs
>sin(x)+sin(x*1.01)
to illustrate

[Anonymous No.10237310]

Can't see shit, everything's blurry

[Anonymous No.10237585]

>>10234471
Mega BUMP

[Anonymous No.10237626]

I've noticed that a little while after urinating in and sealing a piss bottle, the bottle compresses. What's going on here?

[Anonymous No.10237666]

>>10237626
Pressure

[Anonymous No.10237707]

>>10237626
Charles' law
as you pee into the bottle, you are heating up the air in the bottle, as it cools the overall pressure of the air in the bottle will decrease so the atmospheric pressure will compress the bottle until it reaches equilibrium.

[Anonymous No.10237721]

Is there any established convention for the order of operations (i.e. intersection, union...) when writing set theoretical expressions? Should I just assume they have equal precedence and disambiguate with parentheses?

[Anonymous No.10237780]

>>10237721
there is an order of operations for logical connectives like and, or, not, etc, which therefore should also work for set operations. However, nobody knows them, and it just makes it less ambiguous, so just use parentheses

[Anonymous No.10238014]

I've seen the general linear lie algebra defined as the vector space [math] \operatorname{End}(V) [/math] with Lie bracket [math] [x,y]=x\circ y-y\circ x [/math] and as the vector space of [math] n\times n [/math] matrices over [math] \mathbb{F} [/math] with [math] [X,Y]=XY-YX [/math].
Are these equivalent? and if so how do you prove it? i'm aware that linear maps can be represented by matrices, but i wouldnt know where to start with the proof.

[Anonymous No.10238017]

>>10237721
Absolute complement first, all the other operations are equal in precedence.

[Anonymous No.10238021]

>>10237721
I call it BSN
Big symbols, small symbols, not set theory symbols.

[Anonymous No.10238074]

>>10238014
They are not. The second definition does not include the infinite dimension case.

[Anonymous No.10238110]

>>10238014
>how do I prove that linear maps over vector spaces are representable by matrices
It's actually really easy when you actually try. The proof only sucks for modules.

[Anonymous No.10238251]

>>10236948
>>10236957
Sum/product identities:
sin(a+b)=sin(a)*cos(b)+cos(a)*sin(b)
cos(a+b)=cos(a)*cos(b)-sin(a)*sin(b)
Let
p*sin(x)+q*cos(x) = r*sin(x+a)
= r*(sin(x)*cos(a)+cos(x)*sin(a))
= r*cos(a)*sin(x)+r*sin(a)*cos(x)
=> p=r*cos(a), q=r*sin(a)
=>
p^2+q^2=r^2*(cos(a)^2+sin(a)^2)=r^2
q/p = r*sin(a)/r*cos(a) = tan(a)

>>10236979
Again, sum/product identities. The beat frequency is the difference between the two frequencies. If the frequencies are the same then the beat frequency is zero so the modulating signal is a constant.

[None !obkpuSWh5M No.10239211]

>>10238251
What's the best way to learn all the trig identities?

[Anonymous No.10239218]

Is there any career field worth going into without a degree?

[Anonymous No.10239408]

>>10239211
The basic ones derive from the definitions of the various trig functions as the ratios of sides in a right-angled triangle and Pythagoras' theorem. The sum identities can be derived from the fact that if R(x) is a 2x2 matrix corresponding to a rotation by angle x, then R(a+b)=R(a).R(b). The product identities are obtained by calculating sin(a+b)±sin(a-b) (likewise for cos). Multiple angle identities follow from the sum identities (sin(2x)=sin(x+x), sin(3x)=sin(2x+x), etc), half/third/etc angle identities are the inverse (use sin=sqrt(1-cos) to eliminate either sin or cos, square to eliminate the sqrt(), then it's finding the roots of a polynomial).

[Anonymous No.10239419]

>>10234461
if I solve this kinematic quadratic equation, and the result is two positive times, how do I pick which one is correct?

[Anonymous No.10239423]

>>10239419
Forgot pic

[Anonymous No.10239473]

>>10237626
Come on man...

[Anonymous No.10239480]

>>10239419
it's physics. one of the times should seem absurd based on the situation. basically, it'll be obvious.

[Anonymous No.10239500]

Can someone give me a memechart that's actually on point? Pic related doesn't even have book titles/authors. I gotta get my math education up for Max virginity.

[Anonymous No.10239531]

>>10239480
I'm writing a program which calculates time of descent down curves, the curves can also go up at parts, many calculations will be performed and I'm not there to decide every time.

with initial conditions in uniformly accelerated motion being:
velocity(always positive)
accelereation(+or-)
distance(always positive)
how do I pick the correct time?

[Anonymous No.10239537]

>>10239500
Those books are:
Linear Algebra and Geometry - Alexei Kostrikin and Yu Manin
Theorems and Problems in Functional Analysis - Kirillov and Gvishiani
Homotopical Topology - Fomenko and Fuchs
K-Theory - Atiyah
Einstein Manifolds - Arthur Besse
Geometric Topology Localization, Periodicity and Galois Symmetry - Dennis Sullivan
Geometric Invariant Theory - Mumford
Topics in Transcendental Algebraic Geometry - Edited by Phillip Griffiths

[Anonymous No.10239563]

Any advices for learning python 3?
Wiki books are outdated (Python 2)

[Anonymous No.10239605]

>>10239500
>memechart that's on point

[Anonymous No.10239606]

>>10239423
Can that even happen?
Assuming a and d to be positive (if they aren't the result can even be complex), there should be one negative and one positive solution, as the term below the square root is greater then v_0, or am I being stupid.

[Anonymous No.10239618]

>>10239563
>outdated (Python 2)
Despite the name Python 2 is not outdated.

But there are a billion tutorials online to get you started, just start with official one and see if you like it, if not try a different one.

[Anonymous No.10239633]

>>10239537
Wow thanks Anon! This is like an early Christmas present. I can't make any promises but I'll definitely try to follow through.

[Anonymous No.10239666]

>>10239633
I don't actually recommend following that list. I just posted the book titles in that image since you said they weren't visible. The /sci/ wiki has a pretty good list which you can follow.

[Anonymous No.10239668]

>>10239666
Not today satan, it's been spammed so many times I'm doing it for sure.

[Anonymous No.10239736]

>>10239606
d=38.4
a=-1
v0=17.47
try it
acceleration is positive when the object goes uphill

[Anonymous No.10239806]

>>10239736
>a=-1
Obviously it can happen if a is negative.

But in this case the answer has to come from what you are trying to model.

[Anonymous No.10239816]

Silly question, the entropy balance is like that because the entropy remains the same as each cycle ends in the same state as it begins?
Like you get that equation by saying that dS = 0 and :

[eqn]
dS= S{_{in}} - S{_{out}}\geq 0 \\
dS= S{_{in}} - S{_{out}} + S{_{irr}} \\

[Anonymous No.10239820]

Silly question, the entropy balance is like that because the entropy remains the same as each cycle ends in the same state as it begins?
Like you get that equation by saying that dS = 0 and :


[math]
dS= S{_{in}} - S{_{out}}\geq 0 \\
dS= S{_{in}} - S{_{out}} + S{_{irr}} \\
[\math]

[Anonymous No.10239822]

Silly question, the entropy balance is like that because the entropy remains the same as each cycle ends in the same state as it begins?
Like you get that equation by saying that dS = 0 and :


[math]
dS= S{_{in}} - S{_{out}}\geq 0 \\
dS= S{_{in}} - S{_{out}} + S{_{irr}} \\
[/math]

[Anonymous No.10239845]

>>10239822
>entropy
entropy is like evolution, they're useful for making models and coming up with theoretical ideas but neither actually exist in practice

[Anonymous No.10239874]

>>10239845
t. has never read a book

Entropy is a measurable property used to obtain quantitative relations between more tangible quantites like work or pressure for instance

[Anonymous No.10240019]

>>10235337
the details are usually the fun part. if you care more about the big picture than any of the details, you should stick with popsci and do something else for a living. if you ever find the type of details you enjoy, well, there you go, go for it.
but people do these things because they enjoy them. i'm sure you have a hobby or interest that other people might think is absurd. it's kind of like that (but a bit more impassioned)

[Anonymous No.10240106]

>>10239531
plug in both the time values to some position equation and see which one makes sense

[Anonymous No.10240172]

>>10239806
I already said what I'm trying to model
>>10240106
I went with the version where I only use addition and I checked my system for conservation of mechanical energy and it seems to work now fine, just don't know why.

[Anonymous No.10240197]

how do I calculate the input and output impedance of an amplificator?? I saw some excercises, but all of them had bullshit answers

[Anonymous No.10240493]

Is EE more math intensive than aerospace?

[Anonymous No.10240750]

Why is [math]\mu \rightarrow - \infty[/math] the thermodynamic limit in the grand canonical ensemble in statistical mechanics?

[Anonymous No.10241121]

>>10240197
Depends on the circuit. The only general answer is look at the amount of current you get from a certain applied voltage.

>>10240493
Yes

I have a point light source and a plane above it. I'm trying to determine the intensity (mW/mm^2) of the light on the plane as a function of the angle from the vertical. I can't seem to wrap my head around how the radiant intensity and radiant power correspond with each other and with the relative luminous intensity plot. Is it true that [eqn] 2 \pi \int_0^{\pi/2} I_{rel}(\phi)B \sin(\phi) d\phi = P_{tot} [/eqn] where B is a scaling factor?

If so:
- where does the [math] I_{rad} = 2.5 [/math] come into play?
- I'm thinking that after finding B, I can find the change in power (flux) as the angle goes [math] \phi \rightarrow \phi + \Delta\phi [/math]. I can then find the change in the area subtended, which I think is [math] 2\pi r^2 \sin(\phi) \Delta \phi [/math], and I can get the intensity in the new annulus. Is that equal to the intensity in the ring on the plane at that same angle, or do I need to correct it somehow?

[Anonymous No.10241146]

>>10241121
I'm thinking correct it by multiplying by cos(phi). I'm like 80% confident in my logic so if anyone wants to chime in and confirm or dispute anything please do.

[Anonymous No.10241480]

what is the most /sci/ way to commit suicide?

[Anonymous No.10241524]

>https://en.wikipedia.org/wiki/Pyramid_scheme#The_%22eight_ball%22_model

So at least 87.5% of people entering will lose all their money, but how would this compare in terms of odds to betting on a +700 (x8.00) sports bet?

[Anonymous No.10241536]

>>10241480
collapsing the false vacuum.

[Anonymous No.10241555]

Can it be said that there exists a set of all possible sets (and thus all possible values), even though it would by definition contain its own powerset? Is it turtles all the way down?

[Anonymous No.10241557]

>>10241555
>Can it be said that there exists a set of all possible sets
No.

[Anonymous No.10241558]

What's the relationship between relative complements and abjunction?

[Anonymous No.10241996]

Can someone explain the pigeon hole argument for real number set being uncountable? I'm not really sure what it's supposed to do, other than we don't have a good way to count it, not necessarily that there is totally no good way to do it.

[Anonymous No.10241999]

>>10241996
You mean the diagonal slash proof?

[Anonymous No.10242015]

>>10241999
I think so, yeah.

[Anonymous No.10242055]

Any recommended literature or research on iatragenics?

[Anonymous No.10242066]

>>10242015
Any countably infinite list you make of real numbers will always be missing real numbers. If you had a list of every real number between 0 and 1 then you could make a new list by adding a number using the diagonal digits. So you cant ever have a countable list of all real numbers between 0 and 1.

How you count those reals is irrelevant, all you need to assume is that there is a list in the first place.

[Anonymous No.10242067]

>>10242015
First, you need to remember that the fundamental part of an ennumeration is that I can give you any element of the set being ennumerated and you can tell me the natural number that mapped to it.
Cantor showed that if we take any ennumeration of the sequences of 0s and 1s we can take a diagonal slash, and claim that no natural number maps to it, because otherwise we'd have a contradiction. In other words, the ennumeration isn't invertible, and thus, not a bijection.
The set of sequences of 0s and 1s naturally maps to the reals between 0 and 1 by taking powers of two.

[Anonymous No.10242243]

>>10241555
Sets in ZF are forbidden from being elements of themselves by the Axiom of Regularity.

However, in practice, most mathematicians assume (at least implicitly) the existence of a set (or proper class) U large enough to contain all sets of interest to them. U is called a Grothendieck universe and elements of U are called small sets. This allows one to speak meaningfully of things like the category of (small) sets, the category of (small) groups, etc.

[Anonymous No.10242346]

>>10236987
Some schools in the US have a combined BS/MS program where you can earn both degrees in 5 years due to overlapping credits.

[Anonymous No.10242354]

is it actually possible to get aids from pools?

[Anonymous No.10242522]

>>10237721
I'm not a set theory notation expert but I'd give intersections higher precedence than unions since they're analogous to logical conjunction and disjunction respectively, and those have well defined precedence.

[Anonymous No.10242666]

>>10234461
is writing [math](x, \textbf{y})[/math] where [math]\textbf{y}=(y_1,y_2,...,y_n) [/math] the same as writing [math](x, y_1,y_2,...,y_n)[/math] ?

[Anonymous No.10242674]

>>10242666
that seems like an unorthodox way to do it, but I guess it works. what is the context?

[Anonymous No.10242788]

>>10242674
generalization of picard's existence and uniqueness theroem for systems of differential equations using vector notation

Given an initial value problem [math]\textbf y'=\textbf f(x,\textbf y), \textbf y(x_0) = \boldsymbol\gamma[/math], where [math]\textbf f=(f_1, ..., f_n):I\times\mathbb R^n\rightarrow\mathbb R^n[/math] and [math]\boldsymbol\gamma =(\gamma_1, ..., \gamma_n)[/math]

Let every component [math]f_i(x, y_1, ..., y_n)[/math] of function [math]\textbf f(x, \textbf y)[/math] be continuous in a neighborhood of

>[math](x_0, \boldsymbol\gamma)[/math]

Then the IVP has a solution in the neighborhood of [math]x_0[/math]. If the component are also all lipschitz continuous in the neighborhood of

>[math](x_0, \gamma_1,..., \gamma_n)[/math],

then the solution is unique.

[Anonymous No.10242789]

>>10242666
What if it is more like having [math](x,\textbf{y})=((x,y_1),(x,y_2),...,(x,y_n))[/math]

[Anonymous No.10242822]

>>10242788
>>10242666
yes, it's a very common shorthand

technically it should be [math](x,(y_1,...,y_n))[/math], but there is a canonical isomorphism (in any reasonable category, that is, anything actually anyone works in) of [math]I\times (\mathbb R \times... \times\mathbb R)\cong I \times \mathbb R\times ...\times \mathbb R[/math], so in principle, it doesn't matter, but you could be pedantic about it. Again though, nobody cares.

[Anonymous No.10242836]

>>10242674
>>10242789
>>10242822

Okay, thanks a lot.

[Anonymous No.10242968]

>>10240750
Bump

[Anonymous No.10242981]

Something smells quite horrible from the back of my refridgerator. At first I thought it was some old food but I have emptied it now at after I pulled it out it was clear that it's from the back and not the inside. The small thing at the bottom says pentane, could that be leaking and causing it?

It smells kind of sweet but in a disgusting nauesating kind of way.

[Anonymous No.10243008]

Books on Signals and Systems?
Taking a class on it next semester and cant find a syllabus. Want to check it out before the semester starts. Here's are topics of what would show up: Fourier, Laplace and z-transforms, sampling theorem, modulation, system stability, and digital filters

[Anonymous No.10243015]

Long story straight, I sucked at high school due to a lack of discipline, video game addiction, depression, low self esteem etc and as an adult, I'm over all of that and want to go to university. My big problem is that I have NO idea how to study anything effectively. How does /sci/ study?

[Anonymous No.10243033]

>>10243015
Read and do problems

[Anonymous No.10243189]

Has anyone used Gordon Baym's Lectures on Quantum Mechanics for a class? Used it last semester and thought it was crap, I'm trying to figure out if I'm retarded or if I should be using a different book.

[Anonymous No.10243201]

2/(sqrt(2) + 1) = 2sqrt(2) - 2

Is their another way to pass from the left to the right than multiplied by (1 - sqrt(2))/(1 - sqrt(2)) please?
Thank you!

[Anonymous No.10243216]

>>10243201
No. The only way to simplify the denominator is to multiply by k/k for some k which allows the denominator to be simplified. To eliminate the sqrt(), k must include a term which is a multiple of sqrt(2) so that you get sqrt(2)*sqrt(2)=2. If you multiply (sqrt(2)+a)*(sqrt(2)+k), you get a*k+(a+k)*sqrt(2)+2. So the only way to not have a sqrt() term in the result is if a+k=0 => k=-a, i.e. multiply numerator and denominator by sqrt(2)-a.

[Anonymous No.10243220]

>>10243216
ok thanks!

[Anonymous No.10243440]

i need to get a 4.0 next semester
how do i get an A in Physics, Metrology and Calc 2

[Anonymous No.10243456]

>>10234461
If you have already chosen a gold ball then you must have one of the two boxes that contain gold balls. Therefore the probability is 1/2. Nothing else makes a bit of sense, you have to be simultaneously high IQ and stupid to believe that the probability could be anything other than 1/2

Some high IQ brainlet tried to tell me that you use the law of total probability to calculate all the probabilities and then update based on the fact that you chose a gold ball, and somehow you get 2/3. I will tell you why this doesn't make sense:

Do the same problem but you start out with 1,000 boxes that do not contain gold balls and then the two gold ball containing boxes from the original question. or better, take the limit as you approach Infinity number of boxes that do not contain gold balls, you get a different probability every time, even though each repeat of the experiment has you selecting a ball from a box that contains a gold ball, and there will only ever be two of those boxes.
High IQ brainlets that believe this kind of nonsense shut up my math classes when they should be doing engineering or some other baby science.

Somebody tell me why I'm wrong.

[Anonymous No.10243760]

>>10243456
There are six possible scenarios: you pick the leftmost ball, you pick the next one, and so on, and each of these have the same chance of happening. In three of these scenarios you've picked a golden ball. In two of those three scenarions picking another ball means picking a golden ball. Thus, two thirds.
Also, be more polite asking questions.

[Anonymous No.10243791]

>>10243456
> If you have already chosen a gold ball then you must have one of the two boxes that contain gold balls. Therefore the probability is 1/2
Wrong. The probability that you have the box containing 2 gold balls is 2/3, the probability that you have the box containing one gold and one silver is 1/3.

There are 6 equally-likely cases. Box 1 ball 1, box 1 ball 2, box 2 ball 1, box 2 ball 2, box 3 ball 1, box 3 ball 2. The first 3 cases have you draw a gold ball first, the last 3 have you drawing a silver ball first. If you draw a gold ball first, you're constrained to the first 3 cases: box 1 ball 1, box 1 ball 2, box 2 ball 1. The first two cases will have the second ball also be gold (the other ball in box 1), the third case will have the second ball be silver. IOW, 2/3 to 1/3.

> you have to be simultaneously high IQ and stupid to believe that the probability could be anything other than 1/2
You have to be incapable of both math and numerical simulation to think that the probability could be 1/2 . And you'd also need to completely lack any self-awareness to write a screed about how anyone who gets the correct answer must be stupid.

This is about the most basic example possible of conditional probability. P(A|B) = P(A∩B)/P(B). P(A∩B) is the probability that both balls are gold, i.e. the probability that you pick the first box = 1/3. P(B) is the probability the first ball is gold = 1/2. P(A∩B)/P(B) = (1/3)/(1/2)=2/3.

[Anonymous No.10243868]

I feel seriously stupid asking this, but what the fuck does 2 over 5 mean and how do I do this problem? I know it's probably really easy, but I haven't done math in years and never paid attention in math either.

The rest of the question is easy, I just don't get what 2 over 5 means.

[Anonymous No.10243883]

>>10243868
It means 2 divided by 5, which can be written as 0.4 if you are more used to decimals.

[Anonymous No.10243885]

>>10243883
Is there an easy way I can do this in my head without a calculator?

[Anonymous No.10243890]

>>10239408
Any tips that'll help me learn precal in 2 weeks?

[Anonymous No.10243891]

>>10243885
You can multiply or divide with any number you want, as long as you do it to both the upper number (numerator) and the lower number (denominator)

In this example you can multiply both numbers by 2

[math]\frac{2}{5} = \frac{2 \cdot 2}{2 \cdot 5} = \frac{4}{10} = 0.4[/math]

[Anonymous No.10243895]

>>10243891
Thanks anon. Apparently I have a longer road ahead of me than I thought.

[Anonymous No.10243930]

How to (1) find the modulus and argument/angle of [math] z = 1 \angle 158^{\circ }[/math], (2) find [math] z^{10} = (1 \angle 158^{\circ })^{10} [/math] using the De Moivre's formula?

[Anonymous No.10243941]

>>10243930
What have you tried?

[Anonymous No.10244000]

>>10243930
You already have the modulus and argument of z.
Take the tenth power of z's modulus for the modulus of z^10. Multiply 158 by ten and slip it back into 360 for z^10's argument.

[Anonymous No.10244123]

Need some help with the Glicko rating algorithm.
Essentially a player's rating deviation (RD) changes from two things: Played games and the passage of time.
With the latter in mind, when exactly would a player be re-calculated? i.e. they haven't played any games, so their RD should be higher. But when exactly should this RD change be calculated? Would all players in the league be calculated regardless of whether they attended a tournament or not?

[Anonymous No.10244127]

>>10244123
Obviously when someone is interested in knowing his current RD.

[Anonymous No.10244151]

Okay weird question but I just watched my Dad's 100% cotton jumper catch fire from a gas flame, and then it spread up the jumper but died out without burning anything. Can anyone explain what happened?

[Anonymous No.10244160]

>>10244151
Was it new? Had it been washed previously?
Had it happen to me as well and freaked me the fuck out. I guess it's some kind of chemical laced on the shirt for storage or whatever

[Anonymous No.10244253]

>>10244000
Thanks, that makes sense. However, when writing the answer for [math]z^10[/math] should I just write [math]1 \angle 140[/math] or is there some alternative to it?

[Anonymous No.10244261]

>>10244253
I'd write "the modulus of z^10 is 1, and the argument is 140", but that works too.

[Anonymous No.10244348]

>>10237626
>>10237707
Just like this anon said it's Charles' law. Volume and Temperature have a direct relationship. As volume increases, Temperature also increases and vice versa. The equation for Charles' law is V1/T1=V2/T2 (as long as the pressure and gas are constant, for increase of pressure the combined gas law P1V1/T1=P2V2/T2. Remember T is in Kelvin.)

[Anonymous No.10244476]

>>10239218
Clandestine Drug Manufacture (if you are able to adequately teach yourself), Art (if you are talented), Music (band that gets money for small gigs, pianist for events, DJ for events, that chill af saxophonist that gets paid for being smooth in coffee shops/bars), some kind of trade (don't be stupid, find a trade that doesn't primarily work outside so the weather doesn't fuck you, create your own business or be someone's wageslave for piss change ;3), Crypto/Stocks if you can predict, invest, and hold when others panic, or just buy cheap stuff you know has demand and resell it. It's all about finding how to leech off of society but make it look like your income is borderline poverty like all the wageslaves. Some people consider this cheating out of hard work and the bread you get isn't earned but swindled like a scalper or some chink trying to sell you fake Rolex watch. I dismiss these claims as I only have one goal in mind, make a business out of what I have passion for so I don't feel like I want to blow my brains out heading to work even if it is considered wrong by others. The catch is that people will say: "Oh, you haven't actually worked a REAL job before so you are classified by us normies as a degenerate." You have to work a REAL job at some point to break free of the majority degeneracy label. Not working for your parents and them sliding money under the table, a legit job for at least half a year. Thank Christ I am past that already, I used to slam my head against a wall every morning because if I wasn't AWAKE and PAYING ATTENTION I would be let go as I could easily be replaced by someone with a degree. Now I can tell people to fuck off with proof when they say I have contributed nothing to society. It's sad how people make a contest for who has been shit on for the most amount of years working a REAL job. I don't consider that status, just experience to qualify for other less shitty REAL jobs. I would rather take a swing at the dream.

[Anonymous No.10244850]

How do you motivate yourself to study hard? My last exams of my life are coming up but it's hard and so much work. Modafinil / adderall or whatever are unfortunately not an option for me.

[Anonymous No.10244857]

Whats the difference between Lagrange optimization and KKT?

[Anonymous No.10244865]

Anyone familiar with open and closed headphones?
Is it impossible to have closed headphones, which block out sounds, but stlil have a wide and open soundstage similar to open headphones?

[Anonymous No.10244867]

>>10244850
>but it's hard and so much work.
No one said it would be easy. Just do it.
My motivation is to not let my family down. Everyone is smart and I don't want to fall behind. Fun competition.

[Anonymous No.10244872]

>>10243008
bump

[Anonymous No.10244873]

>>10244857
Lagrange only accepts equality constraints.
>>10244850
Pride tbqhwyf.

[Anonymous No.10244884]

>>10243008
Taken from http://4chan-science.wikia.com/wiki/Electrical_and_Electronics_Engineering

[Anonymous No.10244924]

>>10244867
My relationship with family is terrible.
>>10244873
I am ashamed about myself in many ways.

During bachelor years I dealt with depression and almost dropped out more than once. Now my motivation is that once I am done with these exams I only have my master thesis ahead of me. But during my bad time I lost any amount of self discipline and work ethic I ever had. But yeah, you're right. I should just go through with it no matter how shitty I feel because not getting my shit together will just make things worse again. And maybe I should rediscover my sense of pride. Thanks.

[Anonymous No.10244926]

How do I get into Arduino if I know shit about programming?

[Anonymous No.10245065]

Is it possible for a number (x^n) to be divisible by a number that is not a factor of "x"?
How to prove it?

[Anonymous No.10245067]

>>10245065
Yes.
4 is not a factor of 2, and divides 2^2.

[Anonymous No.10245151]

>>10245067
Thank you!
Now:
Is it possible for a number (x^n) to be divisible by a number that is neither a multiple nor a factor of "x"?
If possible, how do I get those numbers?

[Anonymous No.10245230]

>>10245151
>not a multiple
9 is not a factor or twelve, nor is twelve a multiple of 9, but 9 divides twelve squared.
For a to divide x^n, all individual primes that divide a need to divide x. However, they can have different powers. For example, if a=b^2c, and x=bc^2, powers of both are divisible by each other, but neither divides or is a multiple of the other.

[Anonymous No.10245370]

can fourier transform be used to optimise any source code? whether on the same level or going as low as asm/binary

[Anonymous No.10245445]

How do I know if I'm feeling confident or narcissistic? I can't tell if I'm just arrogant or the credit I give myself is legitimately warranted. Should I feel bad about feeling good about my mind?

[Anonymous No.10246008]

>>10245151
Any number can be uniquely factored into powers of primes: 2^a*3^b*5^c*7^d*.... (this is known as the fundamental theorem of arithmetic).

Let e(x,p) denote the exponent of prime p in the factorisation of x. If e(y,p)<=e(x,p) for all p then y divides x. If e(y,p)>=e(x,p) for all p and e(y,p)>e(x,p) for at least one p then y is a multiple of x (the latter requirement is only necessary if you don't consider x itself to be a multiple of x). If e(y,p)<e(x,p) for any p then y isn't a multiple of x. Also, e(x^n,p)=n*e(x,p).

So any number y for which:
e(y,p)<=n*e(x,p) for all p (1)
e(y,p)>e(x,p) for some p (2)
e(y,p)<e(x,p) for some p (3)
satisfies your requirement.

(1) ensures that y divides x^n, (2) ensures that it is not a factor of x, (3) ensures that it is not a multiple of x.

It's possible to satisfy all 3 constraints for any x whose factorisation includes at least two primes. If x is a prime power p^k, then the only numbers which divide x^n=p^(k*n) have the form p^m where m<=k*n, and these are either x (if m=k), factors of x (if m<k) or multiples of x (if m>k).

If x has at least two prime factors p,q (x=p^a*q^b), then y=q^(b+1) divides x^n, isn't a factor of x, and isn't a multiple of x.

[Anonymous No.10246035]

What's the bare minimum atmospheric pressure people can live in for extended periods of time, assuming oxygen concentration can be freely adjusted?

There's a lot of sites talking about barely surviving, but just for a few moments not several weeks or months. I know some human settlements go all the way down to half of sea level pressure, but my guess is that something like the ISS could bring that to a much lower point. As a side question, why does it operate at almost one atm? Wouldn't there be benefits to operating at lower pressures like say reduced risk of explosive decompression?

[Anonymous No.10246056]

>>10245445
There's no universal unit of measure for merit, some may see you as a legend while some will think you're trash, you yourself may think you're hot shit now but can later on start belittling your previous accomplishments. It is what it is, so just try to distinguish the value you give to who you are from what you have done, one should be fixed while the other changes freely.

[Anonymous No.10246163]

>>10246056
I don't have many concrete, real world accomplishments, but I've become today the person I wished I was a few years back. I don't know if it's arrogance in what I think I know, or confidence in what I know I do. My sister told me today that I can come off as arrogant by trying to "turn things into a lesson," but I see it more as imparting things I've learned and the system I understand onto others during conversation.
All that being said, this is good advice regardless so thanks anon

[Anonymous No.10246189]

>>10234461
Can anyone please explain to me the "2m" in the dependency set Dm? Thanks

[Anonymous No.10246197]

I'm going to ask this here because it's kind of /sci/ related, but because most of this board seems more educated than the rest of the site. I want to start university in the middle of the year, but I'm having difficulty picking a subject:

>Interested in computer science, but if I want to do that in the middle of this year, I'll need to learn algebra 1/2, calculus etc, mostly by myself without a strong math background
>Interested in law, however, I hear there's a massive surplus of lawyers these days. Having said that, I could see law being a strength for me because it's reading and remembering things, which I'm good at
>Interested in being a doctor, which I'd only have to learn math, biology or chemistry to apply for it, but apparently they re-teach biology during the first year of medical school at the best university in my state. Like law, it's remembering things that aren't formulas or numbers, which is better for me
>Either way, I'll be doing something difficult, but if I had to say, I'd probably saw law would be easiest for me, while computer science would be the most difficult for me to excel at (at least for now)

What's the best way to pick what I want? I honestly like all of them.

[Anonymous No.10246273]

>>10246197
Doctors actually know literally no math.

[Anonymous No.10246411]

>>10244261
>I'd write "the modulus of z^10 is 1, and the argument is 140"

[Anonymous No.10246425]

I've got a pack of questionlets:
1. Do plants take up ammonia as such or do they need it memed up somehow first?
2. Is there a non-primarily-hydrocarbon biological energy storage? Like, at least 50% of energy coming from something other than carbon or hydrogen and both produced and consumed by same organism.
3. How are potential catalysts for reactions discovered?
4. Are all trees using C3 photosynthesis only?
5. Can virus infection "fail" due to wrong placement of the DNA/RNA?

[Anonymous No.10246685]

On independence of motion...

Does friction in the x direction affect velocity in the y direction? I ask assuming they are perfectly perpendicular.

I thought of this watching a movie the other day and wondered about it.

[Anonymous No.10246693]

>>10246685
friction is multidimensional

[Anonymous No.10246736]

>>10246685
No. Well... It depends.

[Anonymous No.10246754]

>>10246425
Do your own HW

[Anonymous No.10246963]

>>10246754
u wot
Are non-homework questions not allowed in those threads or something like that?

[Anonymous No.10247809]

What molecule is this? Some girl I know has it on her shoulder... Thanks!

[Anonymous No.10248111]

How EXACTLY do contact lenses correct one's vision?

I understand that they focus the light on the retina, but how does putting a thing layer of concave plastic on your eyes do that? Does that 1 mm or less extra layer to your cornea really make that big of a difference?

[Anonymous No.10248112]

>>10248111
fuck, I meant "thin layer", not "thing layer"

[Anonymous No.10248138]

>>10234476
>stop posting anime shit
>4chan

[Anonymous No.10248151]

>>10248111
Contact lenses exaggerated to get the point across. I think this is how they work.

[Anonymous No.10248157]

>>10248151
If you are nearsighted, light rays focus too early within your eye — they form a focus point in front of the retina instead of directly on it. Contact lenses and eyeglasses correct nearsightedness by diverging light rays, which reduces the eye's focusing power. This moves the eye's focus point backward, onto the retina where it belongs.

If you are farsighted, your eye does not have adequate focusing power — light rays fail to form a focus point by the time they reach the retina. Contact lenses and glasses correct farsightedness by converging light rays, which increases the eye's focusing power. This moves the eye's focus point forward, onto the retina.

Source: https://www.allaboutvision.com/contacts/faq/how-contacts-work.htm

TL;DR: contact lenses can correct nearsightedness/shortsightedness AND farsightedness (can't see up close).

So nearsightedness is corrected by having a contact lens that has a more obtuse angle than the eye.

Is farsightedness correct by having a contact lens that has a more acute angle than the eye?!

[Anonymous No.10248170]

Pic related
Is there any sub-equation or relationship between b and c that lets you know if the root of x is an integer?
Is it possible for x to be a positive integer if c is negative?

[Anonymous No.10248192]

>>10234461
OK I've just dunked an excess of iron wire into a jar of aqueous (NH4)2S2O8, can someone tell me what the red/brown particulate is? Is it (mixed) iron oxide? Or is it iron (III) sulphate? If it's the former then I suppose I could change the pH to make it stay as iron sulphate, since I don't think iron oxide will work for what I'm trying to do. I also hope the NH4+ remains as a spectator.

The plan is to use an iron sulphate as a copper etchant, then run a current through the now copper sulphate solution to reduce the copper out onto a copper electrode and turn the reduced iron species back into an oxidised form with a carbon electrode.

[Anonymous No.10248193]

>>10248157
I hope I'm not spreading misinformation, edit also made to the top left.

[Anonymous No.10248195]

>>10248151
culo?

[Anonymous No.10248199]

>>10248195
>culo
What?

What language are you speaking to me in?

[Anonymous No.10248280]

is this the place to ask about astronomy? basically I'm looking to buy my first telescope. I hear the Orion Spaceprobe 3 is the one to get, but since it's a reflector maintenance scares me (delicate mirrors and whatnot). Should I just go for it or should I look for something less delicate/complicated/expensive for my first telescope?

[Anonymous No.10248387]

>>10248170
> Is there any sub-equation or relationship between b and c that lets you know if the root of x is an integer?
(x-p)*(x-q)=x^2-(p+q)*x+p*q
So if you can factor c/a into integers p,q such that their sum p+q=-b/a, then the roots are integers. This is equivalent to ((b/a)/2)^2-(c/a) being a perfect square.

> Is it possible for x to be a positive integer if c is negative?
Sure. E.g. x^2-x-2 => {x=-2,x=1}.

Note that as c/a is the product of the roots, if c/a is negative then you have one positive root and one negative root (and the roots will always be real).

More generally, the first thing you do with a polynomial is divide through by the leading coefficient, i.e. ax^2+bx+c=0 => x^2+(b/a)x+(c/a)=0 => x^2+Bx+C=0 where B=b/a, C=c/a. If that results in non-integer coefficients, then clearly the roots won't be integers.

[Anonymous No.10248393]

>>10248280
seems fine, its a cheap scope so don't expect too much, but you can have a good amount of fun with it.

maintenance isn't really an issue, you will probably just collimate it once and that will be it, and it is way better to go the reflector route than to get a refractor if you're primarily interested in astronomy. To be honest I might even suggest going for a larger telescope if you are serious about it, the benefit of a cheap scope is that it will let you realize that astronomy sucks without dumping too much money into it.

Also somewhat of a warning, a scope isn't necessary to get into astronomy, yeah it will give you more to look at, but it will still feel a lot like a normal stargazing session. If you don't find stargazing interesting without a scope, odds are you won't find it fun with a scope either.

[Anonymous No.10248495]

Most answers to this exercise I've seen reason about the restrictions for entries of matrices in V.

Consider [math]B \in V[/math] and [math]\alpha \in W_i[/math], the eigenspace associated to the eigenvalue [math]c_i[/math]. Then [eqn]A(B\alpha) = BA\alpha = c_i (B\alpha)[/eqn]
so that [math]V\subset\cap L(W_i)[/math] (correct? technically we should convert the problem to being about maps instead of matrices I guess). In fact [math]V = \cap L(W_i)[/math]. Is there a nice way to get [math]\dim V = d_1^2 + \dots + d_k^2[/math] from [math]\cap L(W_i)[/math] without matrix arguments?

[Anonymous No.10248644]

In ABCD tetragon E and F are mid points of AB and AD respectively. CF
intersects BD at G point. If and the area of ABCD is 24 , what is
the area of ABCG ?

[Anonymous No.10248776]

>>10248495
Can't you argue something like:

Consider [math]A[/math] to be the matrix with [math]A=\text{Diag}(c_1,...c_1,c_2,...,c_2,...,c_k,...,c_k,0,...,0)[/math] (ie, the entries ordered by their label and multiplicity and the rest 0s). Each set of entries corresponding to some [math]c_i[/math] correspond to a [math]d_i\times d_i[/math] block [math]c_i I[/math], so [math]A=\text{Diag}(c_1 I,...,c_k I,0)[/math]. Now the space [math]V[/math] can be taken instead to be the space of matrices that block-wise commute with [math]A[/math]. Since each non-zero block [math]c_i I[/math] is a scalar amount of the identity, it defines a subspace of [math]V[/math] consisting of all matrices that are [math]0[/math] everywhere but not on the corresponding [math]d_i\times d_i[/math] block. This subspace obviously has dimension [math]d_i^2[/math], and it defines [math]k[/math] such subspaces for each [math]c_i[/math], so the total dimension of [math]V[/math] must be [math]d_1^2+...+d_k^2[/math].

I know this isn't a particular non-matrix argument, but you can easily turn it into a geometric one.

[Anonymous No.10248781]

>>10248495
>the space of nxn matrices such that AB=BA
That's what I colloquially call an extremely strong statement that you don't immediately notice.

[Anonymous No.10248861]

>>10248393
thanks family
my other option is the celestron 127. It's far more popular on the internet, which one you think will give me a better image?
I live in Chile btw, people keep yapping about "muh clear skies" and "muh highest telescope per capita in the world" and whatnot. You'd think that makes telescopes here cheaper but hell no.

[Anonymous No.10248959]

>>10234461
(Potentially) silly math question.

Is it possible to geometrically (and/or topographically) average together two shapes/morphs? Like, can I take the average "shape" of a triangle and a pentagon and get a square?

Is there a proper mathematical way of doing this, aside from my caveman "3 corners + 5 corners = 8 corners / 2 = 4 corners = square"?

[Anonymous No.10248960]

>>10234461
how 2 get smarts

[Anonymous No.10249012]

>>10248959
If you are smart enough to ask this question you are smart enough to answer it too.

[Anonymous No.10249037]

>>10248959
>>10249012
I'm flattered, but I'm probably not smart enough to answer it. I'll try though and you can tell me if I'm right.

For 2d shapes, if you average the area and perimeter of the shapes, then you have a constriction on the area and perimeter.

With these, you can probably guess the shape it'll be by averaging corners, but is there a way to use calculus for this? Like setting an equation of some derivative to 0?

Also doesn't say how'd it work in three dimensions.

[Tuba Jam No.10249052]

>>10248959
hint: begin by overlapping the shapes by moving their center points so that the center points coincide and setting their areas to be equal.

[Anonymous No.10249142]

How did the author come up with the differential equations in the image? (he uses the superscript in $ v_1^{(1)}(t) $ to denote first derivative.

[Anonymous No.10249162]

>>10249142
The current through [math] C_1 [/math] is [math] i_1 = C_1 v_1^{(1)} [/math] and [math] i_1 = (v_2 - v_1)/R_3 + (e_1 - v_1)/R_1[/math] by KCL. Similarly for the other node.

[Anonymous No.10249164]

What math do I need to know to solve the rational distance problem for the unit square?

[Anonymous No.10249166]

>>10249162
would u recommend any book to learn the techniques? I am self-taught...

[Anonymous No.10249170]

>>10249166
It's just repeated application of KCL and/or KVL. Maybe you can look at Fundamentals of Electric Circuits by Sadiku.

[Anonymous No.10249180]

>>10249164
It should come from either analytic geometry, synthetic geometry, calculus, field theory, galois theory, algebraic geometry, inverse galois theory, elliptic curves, or some other subject I don't know.
My main guess for the solution is honestly Galois theory. The whole "one solution implies four solutions" thing.

[Anonymous No.10249184]

>>10249170
thx anon

[Anonymous No.10249212]

8 days after lastday of finals, professor still hasnt posted finals or tests from the semester. What the fuck???

[Anonymous No.10249230]

>>10249052
What do you mean set areas to be equal, just give them both the average?
Without doing anything on paper, do you mean to imply that (in the example of the Triangle+Circle=Square), there will be an intersection of perimeters such that they make contact at four points?

[Anonymous No.10249237]

>>10248959
Read up on simplexes.
Otherwise, I don't really know what you want. A function that maps pairs of polygons onto a random polygon with average number of sides is easy, but that has no useful or interesting properties.
What else do you want this function to do? Average areas? Perimeters?

[Anonymous No.10249251]

>>10249237
I want to prove the average of a Triangle and a Pentagon is a square.

[Anonymous No.10249256]

>>10249251
"Average" is a function defined on the cartesian products of the real numbers. There is no equivalent of it to polygons. You don't want to prove anything, you're building a definition. What I'm asking is what kind of definition you want it to be, exactly.

[Anonymous No.10249263]

>>10249256
That's the tricky part, I don't know. Conceptually, you can see what I'm going for. it makes since than the average of a three sided and a five sided polygon would be a four sided one right?
The most boring definition would be average the numbers of corners and areas and then make the shape from that.

[Anonymous No.10249365]

>>10248170
Sure.

Let b=2ab' and c=-c' where c' is a positive integer. Then the quadratic equation takes the form:

x=-b'+(b'+c'\a)^{1\2}.

Assume c'/a=b'd, where d is a positive integer. We have:

x=b'(-1+(1+d)^{1\2}).

Obviously, we select a d belonging to the set of perfect squares minus 1 eg (3,15,24,...). Hence, x is an integer so long as d belongs to this set.

[Anonymous No.10249738]

I'm doing math but I hate using paper and pencil to work out shit. Is there like some software I can punch in an equation with commands like

"Divide both sides by x" or "replace the numerator with this"

and it will spit out a new, reformed equation?

[Anonymous No.10249760]

>>10249738

[Anonymous No.10249879]

>>10249738
LaTeX, also Grapher on MacOS.

[Anonymous No.10249905]

>>10249879

Isn't latex just for representing formula? How exactly is it going to do the complicated function of dividing out common factors?

[Anonymous No.10249928]

>>10249905
>the complicated function of dividing out common factors

[Anonymous No.10250039]

>>10249738
maxima

[Anonymous No.10250094]

>>10250039

Thanks friend

[Anonymous No.10250323]

>>10248781
Yeah, until you notice that A is a diagonal matrix, not so strong anymore

[Anonymous No.10250342]

>>10248861
>which one you think will give me a better image?
there won't be any noticeable difference in viewing the planets and the moon between these telescopes, but the celestron would give you much more viewing options for deep sky objects (nebulae, clusters, galaxies). If you have really good viewing conditions (can see the milky way at night and clear skies aren't rare) the celestron seems like a better starting scope, perhaps you could go even bigger. However if you do decide to go with the Orion, don't feel like your missing out on much, you will still have more power than Galileo ever did and he devoted his whole life to astronomy

[Anonymous No.10250475]

Is there an equation to get just the 2 closest factors of a number ?
like, having the factors of 52, {1,2,4,13,26,52},
Is there an equation to get just 4 and 13 without having to divide 52 by every single integer from 1 to 13?

[Anonymous No.10250484]

>>10250475
yes, you could divide 52 by every integer between 14 and 52.

[Anonymous No.10250534]

>>10250484
that doesn't get just 4 and 13

[Anonymous No.10250544]

>>10250475
>two closest factors
That would be 1 and 2.
Unless you're using a definition of factor other than "number that divides this other number" and/or of difference than "a-b"

[Anonymous No.10250556]

>>10250475
you just need to find the largest factor of A thats less than or equal to sqrtA, and then the other factor is A/factor

[Anonymous No.10250559]

>>10250475
No I don't think so but if you can come up with one you'd probably have to use the Euler phi function or something similar.

[Anonymous No.10250560]

>>10250544
>googles factor to make sure
>a factor is actually a member of a duo of numbers that multiply by each other to get an original number
English is a weird language.
>>10250556
This.

[Anonymous No.10250574]

>>10250556
THANK YOU
How did you do it?
Can I see proofs?

[Anonymous No.10250577]

>>10250556
But how does that guarantee they're he closest together?

[Anonymous No.10250579]

>>10250574
Not that guy.
>let a be the largest divisor of A that is smaller than the root of A
>let b be the the smallest divisor of A that is larger than the root of A
>ab=A
Proof is obvious and left to the reader.

[Anonymous No.10250600]

not rigorous because i hate number theory, sorry
>>10250574
>>10250577

[Anonymous No.10251130]

>>10250577
Divisors come in pairs. If a is a divisor of x then so is x/a. If b is also a divisor such that b<a, then x/b>x/a.

x/a=sqrt(x)*sqrt(x)/a; if a<sqrt(x), sqrt(x)/a>1 => x/a > sqrt(x). So one divisor will always be less than or equal to sqrt(x) and the other greater than or equal to it (if x is a perfect square, its square root is an integer so it can be factored as sqrt(x)*sqrt(x)).

So the closest pair consists of the largest divisor <= sqrt(x) and the smallest divisor >= sqrt(x).

On a logarithmic scale, the divisors are symmetric about sqrt(x). (log(a)+log(x/a))/2 = log(a*x/a)/2 = log(x)/2 = log(sqrt(x)).

[Anonymous No.10251137]

>>10239845
>hello creatard my old friend

[Anonymous No.10251510]

How the fuck does this jump even work?

[Anonymous No.10251548]

>>10251510
[math] \phi [/math] and [math] \psi [/math] are roots of [math] x^2 - x - 1 [/math].

[Anonymous No.10251887]

Hi, branilet here. How do I figure out what the sigma formula is for the following summation pattern: 2*3+3*5+4*7+5*9+6*11 ?

[Anonymous No.10251918]

>>10251887
First, look at it as two sequences, the number multiplying on the left, and the one on the right.
So you've got two sequences: 2, 3, 4, 5, 6, ..., and 3, 5, 7, 9, 11...
Set one of them as sequence a indexed by i, another as b also indexed by i, and then let the sigma be the summation of pointwise multiplication.
Extra tip: interpreting 2 and 3 as the second elements of their sequences leads to a prettier formula.

[Anonymous No.10251991]

>>10251918
>let the sigma be the summation of pointwise multiplication
Don't understand what that means. What's the sigma formula? It's better to just reverse engineer it.

[Anonymous No.10251999]

Yo fellas, think you could help a stupid nigga out? Would anyone be able to explain the equation for the loss of kinetic energy of a projectile after it ricochets off of a surface?

[Anonymous No.10252008]

>>10251991
As in, we set [math]\sum a_ib_i[/math], where [math]a_i[/math] denotes the i element of the sequence a, and similarly for b, and finally a is the sequence 2, 3, 4, 5, ..., and b is the sequence 3, 5, 7, ...

[Anonymous No.10252027]

>>10252008
Is there no straight formula? Similar to i(i+1) = 2*3+3*4+4*5+5*6

[Anonymous No.10252067]

>>10252027
That‘s what the other guy is trying to prod you towards. [math]\sum_{i=2}^{6} i \cdot (2i-1)[/math]

[Anonymous No.10252105]

>>10252067
Thank you.

[Anonymous No.10252278]

Hi, Brainlet here. How are [math] \neg \forall (x) P(x) \forall (x) \neg P(x) [/math] not logically equivalent ?

[Anonymous No.10252285]

Hi, Brainlet here. How are Hi, Brainlet here. How are :

[math] \neg (\forall x) P(x)[\math]
[math] (\forall x) \neg P(x)[\math]

not logically equivalent ?

[Anonymous No.10252816]

So why does my evolutionary algorithm for finding the brachistochrone(curve of fastest descent) converge on this local minima and not follow a nice curve from A to B, and how do I fix this

[Anonymous No.10252861]

>>10252816
That's literally what it's supposed to look like.

[Anonymous No.10252901]

>>10252816
Looks like you didn't define your boundary conditions properly.

[Anonymous No.10253094]

Is there an efficient way to combine thousands of html pages into an epub/pdf? The existing PDFs for this:
feynmanlectures.caltech.edu/
are unsatisfatory to me.

[Anonymous No.10253103]

>>10253094
I think this is a question better asked at /g/sqt.

[Anonymous No.10253115]

>>10253103
I posted both places

[Anonymous No.10253118]

>>10253094
Download Calibre and fiddle around until it comes out the way you want.

[Anonymous No.10253122]

>>10253118
retard

[Anonymous No.10253173]

>>10253115
For doing that to doujin images, I opened the lot in Apple's Preview application, and saved the whole thing as a PDF through the print screen after making a custom page size for it, not sure if the same can be done with HTMLs or on another OS.

[Anonymous No.10253234]

>>10241536
>not spilling your spaghetti while being spaghettified.

[Anonymous No.10253290]

>>10250342
thanks again family. I took your advice and decided to look a biut further, and I ran into these other brand (Barride Optics, they sell as "Omegon" in some parts of the world it seems) and those are as close as reasonably priced as I've seen here. Ever.
Anyway I got in touch with one of their sellers and he offered me pic related (new) for the same price the celestron 127eq goes here used.
There's very little info on this brand out there (as in, reviews) but all is positive.

On the other hand, I've started to think maybe I should go slow and get something like the celestron 60AZ. Those go dirt cheap and will suffice to show me if I'm actually into astronomy.. or not?
I just don't want to screw up.
Any reply will be appreciated, thanks

Here's the link for the barride 750/150: http://www.barride-optics.com/html/Astronomical-Telescope_Reflector-Telescope_181.html

[Anonymous No.10253426]

>>10234461
Do rockets experience ground effect? I know its reactionary but does the pressure difference have any noticeable effect?

[Anonymous No.10253505]

[math] V = I Z [/math] where V, I, and Z are complex, so [math] Z = \frac{V}{I}[/math]. My thinking is that I can take the Fourier transform of V and I and get [math] Z(f) = \frac{V_{fft}}{I_{fft}} [/math]. But for some reason the Z I get from this procedure is the complex conjugate of what it should be. Anyone know why?

[Anonymous No.10254086]

>>10252861
no it's supposed to be a cycloid

[Anonymous No.10254231]

Regarding heat transfer, you always see 3 kinds listed, conduction, convection and radiation.
Isn't convection just a special case of conduction? Why is it always listed independently?

[Anonymous No.10254357]

Given the polynomial [math]a^{10}+a^5+1[/math], can you instantly tell that it has a factor [math]a^2+a+1[/math]?
If yes, how?

[Anonymous No.10254373]

>>10254357
Yes, because the roots of [math] a^2 + a + 1[/math] are the non-trivial roots of [math] x^3 - 1 [/math] and these are also roots of [math] a^10 + a^5 + 1 [/math].

[Anonymous No.10254375]

>>10254357
Set [math]b=a^5[/math]. This gives us the polynomial [math]b^2+b+1[/math], solvable for [math]b'=-(-1)^{1/3}[/math] and [math]b''=(-1)^2/3[/math].
Setting [math]a^5=b'[/math] and [math]a^5=b''[/math] gives us two easy to solve polynomials.
>>10254373
Reminder that ^ without the keys takes only the first letter/number/symbol.

[Anonymous No.10254391]

>>10254375
>Reminder that ^ without the keys takes only the first letter/number/symbol.
Ah yes you made a similar typo in your post too lol

[Anonymous No.10254464]

What the fuck is this shit? I just got taught how to do pV diagrams by using the integral of V in respect to p, and now they throw this shit in my face?

How can i even know this?

[Anonymous No.10254470]

>>10254464
Isn't the work the difference of temperatures in energy?
t. not a physicist

[Anonymous No.10254482]

>>10254470
No, since the first law of thermodynamics also state that the energy could be kinetic (you're describing Q in delta U = W + Q). That's where the volume comes in

[Anonymous No.10254590]

Can force ever be applied without work naturally? Can you provide an example if it can?

This is not for school. I don't go to school.
>2018
>still going to the Academic Jew

[Anonymous No.10254596]

>>10254590
Push on your local coffee mug without actually moving it. You're applying force to the mug, but since it's not moving, no work is being done.

[Anonymous No.10254597]

>>10254590
what I mean to say is can a force ever be separate from work?

[Anonymous No.10254604]

>>10254597
>can a force not do work?
Yes, if the object remains stationary. Say, try to push a wall. You're obviously producing a force, since it's pushing you back, but the concrete laughs at you.

[Anonymous No.10254619]

>>10254596
I have been pushing my local coffee mug, wondering about a few things. Maybe from the mug's frame of reference there is no displacement, but my finger tip compresses and my finger bends, just as I am about to overcome the mug's friction. Isn't this displacement of the hand or am I a brainlet?

[Anonymous No.10254626]

>>10254619
Push on it with your cellphone, or with a rock, or with a diamond, or something in compressible. The effect is the same; you're applying force, but no work is done, since statistical friction counteracts it.

Another thing: hold the mug still in the air. If you DONT hold it, it'll fall down because of gravity. So you're applying a force to the mug. But the mug is stationary, you're holding it in the air, so again no work is being done, but you're applying a force to the object. Also see previously mentioned example with applying force to a wall.

[Anonymous No.10254661]

>>10254626
But if you apply a force, haven't you accelerated mass? If the mass doesn't move, where is the acceleration?

[Anonymous No.10254672]

>>10254661
Resultant force is mass times acceleration, not force. The sum of forces gives resultant force.
>inb4 so I can claim there are two exact opposite forces pushing on everything all the time and Newton literally can't counterargue?
Yes, that's the half the meaning of relative in Newton.

[Anonymous No.10254696]

>>10254672
Please elaborate. I can't see how your post relates to mine.

[Anonymous No.10255081]

I took my first course in abstract algebra last year and I studied basic group theory. I would like to know more about group theory which books do you recommend?

[Anonymous No.10255092]

>>10255081
Grillet's Abstract Algebra, Lang's Algebra, or whatever other 600 pages graduate level text should fill most of the gaps before you can go for:
-The literal ennumeration of the simple groups. (springer has a book called "The simple groups" that I haven't read)
-Representation theory
-Inverse Galois theory (essentially, "nice group you've got there, is it the Galois group of some field extension?")
-Algebraic topology

[Anonymous No.10255141]

>>10255092
thx fren

[Anonymous No.10255412]

How would I go about cloning a dead dog from it's DNA?

[Anonymous No.10255443]

>>10255412
You can't clone mammals.

[Anonymous No.10255537]

>>10255443
wtf are you talking about, they cloned a sheep?

[Anonymous No.10255546]

>>10255412
Those Korean guys. I thought you said a dead frog at first, and was about to answer for that animal.

[Anonymous No.10255767]

>>10255081
Group theory is boring af. Other dude pointed out topics in group theory, but there's no point in doing, say, inverse galois theory if you don't know "forward" galois theory, which takes a bit to develop, and similarly for algebraic topology (which i wouldn't really call it group theory since it's usually abelian groups, but sure). You should really learn the classic abstract algebra path before you attempt to continue in any single of the topics. So you should read on basic ring and field theory, perhaps some module and galois theory too. Galois was the first person to (implicitly) use groups and hence serves as a huge motivation as to why anyone would study non-abelian groups in the first place.

Best advice for someone self-studying: pick a short book. Long books will kill all your motivation. The only reason for their existence is as a reference or for an expert to base their class on.

All that said, just go to any good university's page and look for an abstract algebra course notes. Follow it, attempt all the proofs and homework questions and then if you still want to continue with group theory, Rotman's group theory is a classic intro text that goes pretty in depth.

[Anonymous No.10256153]

>>10234461
I just got an infrared thermometer and I feel like it might be giving me incorrect readings.
Can anyone one think of something I can read that can prove or disprove this?

Also, any tips for measuring hot water temps? I know this isn't the best tool for it, but I should be able to get somewhat close, no?

[Anonymous No.10256287]

>>10256153
Update: did some testing all readings are fine and confirmed except hot water in a mug.
Surface temp is much colder than internal.
Obviously that makes sense, just a larger gap than I imagined ~5° - 10° F.

[Anonymous No.10256312]

t. brainlet.
>Didn't study when I was younger and I was supposed to.
>Can't go to a college yet because reasons.

How feasible is to start learning physics by myself? I know realistically i'd have to attend a college eventually, but how far can I get before that and where should I start?

[Anonymous No.10257451]

>>10255537
It died shortly after.

[Anonymous No.10257899]

>>10234461
>>10234461
could someone give me an example of a set of linearly independent finite set of vectors, where some of the vectors are NOT orthogonal? not a problem question, just curious

[Anonymous No.10257911]

>>10257899
>set of linearly independent finite set of vectors, where some of the vectors are NOT orthogonal
oh fuck me, 1,1 and 1,0 in RxR will do the trick.

[Anonymous No.10258153]

>>10256312
Maybe try all the math you don't know with Khan Academy and just work on Young and Freedman Universitary Physics, really reading carefully and doing the most of exercises adn problems that you can. How far? i don't have a clue nor you, maybe. If you are motivated just enjoy

[Anonymous No.10258173]

>>10234461
I'm really fucking dumb, I did this dna extraction experiment from Nile Red's video but I don't know what to do with the resulting solution. I did it since it was relatively cheap and simple to do, but now I've got this solution of strawberry, water, soap, isopropanol and salt and I don't know what to do with it.
Is there a way that doesn't involve distillation to extract the isopropanol from the solution?
Video for reference:https://youtu.be/araeHtN_3Lk

[Anonymous No.10258196]

>>10254661
You have a point "but don't think about it". And study until you know why it works, thinks usually have an explanation far down the road. If it don't, congratulations! But 300+ year old science usually has a solid footing

[Anonymous No.10259416]

So why can't I just do "3 divided by 7 x 14" to get the answer? Why do I get something completely different than what I'm meant to get? What am I not understanding?

[Anonymous No.10259428]

>>10259416
Never mind guys, for some reason it worked. It must just be my calculator.

[Anonymous No.10259481]

>>10259428
You don't need a calculator. 14/7 = 2 so the first term equals 6, and for the 2nd one the two 8s cancel out, so you get 6 + 8 = 14

[Anonymous No.10259484]

>>10259481
You don't need a calculator. 14/7 = 2 so the first term equals 6, and for the 2nd one the two 8s cancel out, so you get 6 + 5= 11

[Anonymous No.10259609]

Why does the points at which a house's AC supply is at 0 current not interrupt some household electrical items? I know the frequency is high but why doesn't that short time of no electricity not matter?

[Anonymous No.10259706]

I know it's a long shot but I'd be really grateful if someone here knew how to construct transportation networks in GAP

https://math.stackexchange.com/questions/3058518/transport-flow-network-in-gap

[Anonymous No.10259736]

>>10254661
if an object doesn't move, it deforms. That deformation might be very small, but it still deforms, thus there is work done, >>10254604 is wrong, in his case, work is done it's just very small to really matter

[Anonymous No.10260499]

>>10260417

[Anonymous No.10260674]

A line integral measures the work done by the vector field. So if I push a box along some curve, the vector field to integrate will be everywhere tangent to the curve, right ?

[Anonymous No.10260725]

>>10260674
It's more along the lines of "the only part that's integrated is the tangent part".

[Anonymous No.10260742]

>>10260674
You're usually integrating the dot product of the field with the tangent direction. The field itself typically won't be tangential to the line.

[Anonymous No.10260863]

>>10244926
The Arduino documentation and online forums make it easy to find what functions to use in any certain circumstance.

As far as general programming knowledge goes (logic, loops, variables, functions) a simple C++ introduction would probably be all you needed to get started.

[Anonymous No.10260868]

>>10234461
Is this board always such a virgin STEM circlejerk? I've never really bothered with /sci/ because I assumed pseudo intellectual college freshmen talk about CS and Maths, while memeing about "bad universities", but it's even worse than I had feared. What the hell is wrong with you Americans?

[Anonymous No.10260980]

Can someone please answer question from this thread-

>>10260958

[Anonymous No.10260989]

>>10260980
http://lmgtfy.com/?q=wireless+power

[Anonymous No.10261033]

>>10260980
The problem with (far) UV is that it's intrinsically ionising. Smaller than ~320nm light has enough energy to kick electrons off ceasium at 3.89eV, and at ~120nm UV has enough energy to ionise common oxygen at 10eV. This ionisation messes with the chemistry of the light collector, so unless you build it out of elements that are difficult to ionise or somehow allow a mode of controllable ionisation as the method of energy collection, your solar cell is going to degrade. And this holds especially true when it comes to plantlife.

But up to 200nm or so it shouldn't be too difficult for such an evolution to take place provided the plant evolves on a planet with plenty of UV light incident on it, but here on Earth we get far more yellow light than UV hence making it a useless niche.

[Anonymous No.10261269]

>>10258196
t. retard

>>10259736
So does that mean, there is never a force which does not do work?

[Anonymous No.10261275]

>>10261269
>So does that mean, there is never a force which does not do work?
I'd say yes, all forces do work

[Anonymous No.10261383]

>>10261275
thanks, fren, Is all work done in time, or is there any instantaneous work?

[Anonymous No.10261403]

>>10261383
well, I have never thought about that aspect since i never needed it, but i guess nothing is "instantaneous". It must take at least a quantum of time. it really depends on what problem you're trying to solve

[Anonymous No.10261570]

>>10261275
A balanced force in an unchanging system isn't doing any work, though you could say that the force did work in the past. Such as the EM force in an atom between the nucleus and electron. If there is no stimulation of the electron levels then no work is done. And arguably, even if an electron was stimulated, the energy stored and released by the EM force wouldn't be classified as work, since the electron doesn't properly accelerate, it just changes its waveform.

[Anonymous No.10261656]

>>10260989
>>10261033
thanks boys

[Anonymous No.10262193]

So if lifting grows your muscles through microtears in the fibers and then rebuilding, could it be possible to use something like a laser to induce microtears in muscle fiber and emulate that lifting experience without actually lifting? basically grow muscles without having to put in hard work?

[Anonymous No.10262222]

>>10262193
Look into TENS units, though more correctly it's EMS units you need.

[Anonymous No.10262385]

I've never studied chemistry in my life, so forgive me if this is a stupid question. Regarding the use of "significant figures," why must I round when I know the exact answer? Why can't I just use the exact answer? It seems to me that I am being forced to use a convoluted manner of approximating what is ultimately a less accurate answer. I find it rather infuriating, actually, so I'm hoping that there is a good reason for it.

[Anonymous No.10262399]

>>10262385
Doing calculations with 15 digit numbers sucks, and measures are often imprecise, so rounding down just takes away the numbers most likely to be wrong.
Another problem is that if you use say, 3.14 for pi, you need to pretty much always cut a few digits at the end of any operations you do with it, otherwise you'll just be working with false precisions.

[Anonymous No.10262416]

>>10262399
So, it's because the perfection of mathematically derived answers does not reflect the imprecise reality?

[Anonymous No.10262423]

>>10262416
That's about it.

[Anonymous No.10262437]

>>10261570
>A balanced force in an unchanging system isn't doing any work
sure, I'm just not sure there is a truly unchanging system (it might be changing on a scale we're not able to even detect), but I might be wrong of course.
>EM force wouldn't be classified as work, since the electron doesn't properly accelerate, it just changes its waveform
why would that not be classified as work?

[Anonymous No.10262498]

Any recommendations for a good textbook for learning Russian with no experience in the language?

English is my primary language

[Anonymous No.10262683]

>>10234461
where is the mistake in my gravity simulation code
on the pic as you can see it doesn't look quite right
here's the code:
https://pastebin.com/2rZfjpB8

[Anonymous No.10262693]

>>10262498
>>>/int/lang
>>>/t/language

[Anonymous No.10262713]

>>10262683
>d=sqrt(x*x)+y*y;
should be
sqrt(x*x+y*y);

[Anonymous No.10262803]

>>10262193
perhaps, but a laser might only effect the outer layer of muscle, while muscles in general are quite large and deep, so (unless you destroy all your outer muscle), you would never "exercise" those inner parts, which is the majority of the muscle.

[Anonymous No.10263000]

So I've got an USB powered speaker with an 3.5 mm audio jack.
I put the USB to the computer and touched the jack and got a slight shock.
Is this a grounding issue?
Why did I get a shock when the jack is supposed to be input, not output?

[Anonymous No.10263050]

>>10262713
Thanks man you saved me. would've taken me forever to notice that
Does anybody know where to place the body and what velocity to give to it so it doesn't precess but just follows an ellipse,is the precession in my case an approximation error maybe?

[Anonymous No.10263063]

>>10263050
pic related

[Anonymous No.10263086]

>>10262683
Also:
> a=1/radius*radius
is parsed as a=(1/radius)*radius which is roughly equivalent to a=1 (except for rounding error). You want a=1/(radius*radius).

Other than that, your calculations could be simplified somewhat to
> r3 = radius * radius * radius
> ax = -x/r3
> ay = -y/r3
This avoids the need to consider the signs of x and y explicitly.

Ultimately, numerical integration will accumulate rounding errors, resulting in drift over time. You can reduce this by using a more accurate estimate of the mean acceleration (and velocity) over the interval rather than just using the final (or initial) value.

[Anonymous No.10263247]

>>10263000
have you ever touched a shopping cart before?

[Anonymous No.10263262]

>>10259609
three-phase. light bulbs still dim as current approaches 0

[Anonymous No.10263305]

>>10260868
>science board on 4channel
>not expecting nerds and autism
Are you actually retarded?

[Anonymous No.10263322]

>>10263000
Most switching PSUs have the DC ground rail connected to the AC live (hot) and neutral rails via capacitors. This effectively puts the DC ground at half mains voltage, albeit with a very high impedance.

[Anonymous No.10263334]

How do I properly budget myself?

[Anonymous No.10263342]

>>10263334
Don't spend

[Anonymous No.10263344]

>>10263334
Literally just write down at the beginning of the month what you plan to do with your paycheck. Then actually do it.

[Anonymous No.10263345]

is the moon landing real?
how did they get from the moon to earth in 3 and a half days? it would've taken like avg 3000mph speed, if so how did they reach that speed?

[Anonymous No.10263353]

new thread
>>10263351
new thread
>>10263351

[Anonymous No.10263381]

>>10263086
I changed the acceleration term like you said and now it works perfectly. later I'll probably add verlet algorithm for better approximation

[Anonymous No.10263818]

>>10262437
Well work in particular is energy used by "W = Fd", so if your force doesn't actually move something it can't be considered work. (the average position of the electron doesn't change either).

>>10263322
>he doesn't have a ground lug on his PSUs
Is this a burger thing?

[Anonymous No.10264004]

>>10263818
But if there is no movement, there is no acceleration, and how can there be a force without acceleration?

[Anonymous No.10264008]

>>10263063
A bigger orbit? Bigger initial radius

[Anonymous No.10264037]

>>10264004
Balanced forces are still forces.

[Anonymous No.10264103]

>>10263345
Rockets

[Anonymous No.10264360]

How do we communicate with space probes in our solar system?
I know it's by radio waves, but how to fuck do you aim your emitter so insanely accurately that you contact a tiny probe that's a billion kilometres away?

[Anonymous No.10265408]

>>10243008
>>10244884
oppenheim's book is fantastic tbqh. i dont like allen and mills.

t. EE PhD.

[Anonymous No.10266044]

>>10259609
For "dumb" devices like toasters and light bulbs, you can think that the device really is switching on and off at that speed, and a high-frequency camera would show you flickering.

Most electronics, like computers, clocks, etc. convert the AC to DC. This is what happens in the "wall wart" on many electronics, or in your computer's PSU. Part of this circuit is a capacitor that stores charge between each peak and "smooths" the wave out.

Three phase is kinda unrelated since you asked about household items. That's a system used for some industrial devices.