/sqt/ Stupid Questions Thread

This thread is for questions that don't deserve their own thread.
>give context
>describe your thought process if you're stuck
>try wolframalpha.com and stackexchange.com
>How To Ask Questions The Smart Way catb.org/~esr/faqs/smart-questions.html
Previous thread

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Other urls found in this thread:

en.wikipedia.org/wiki/Shell_theorem
amazon.com/Way-Remember-History-Mathematics-V/dp/0821806335
en.wikipedia.org/wiki/Integer
twitter.com/SFWRedditImages

Explain elementary proportions to me.

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Can someone explain to me what the real issue is holding up the proof of the reimplantar hypothesis? Or some good intro papers or texts? I’d like to understand it

I recently heard about it and kinda became interested in it because of how simple the original euler zeta function was. But I also found out it’s a meme... so it’s hard to get good resources from people.

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*Reimman

Sorry

Do you have to be a far-right douchebag in order to love science?

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want fuck laura southern.. must donate to patreon accunt..

Yeah dude, I'm gonna go empty my paycheck in there so maybe she'll look at me

Is it normal to hate Analysis?

Riemann*

no real men love anal

This is a problem on my complex analysis class. Given a Riemann Surface W_0 and a compact subset K_0 such that the Riemann Surface W = W_0 \ K_0 there's a point in W say p_0 such that a local barrier exists. Show that Green's function exists.

I tried looking at the solution over the complex plane, Ahlfors creates these two functions that bound the supremum of harmonic functions (Lemma's 1 and 2 around page 240-250 3rd edition) but the problem is the corresponding class of harmonic functions over Riemann surfaces has this log(z(p)) part where z is a coordinate map so it's very difficult to bound. I think you'd have to use the fact K_0 is compact but I'm not sure how. Any anons have some tips?

Pic related #3

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Didn't get an answer for this on the last thread, how do I apply algebraic structure (that of abstract algebra) to the surfaces of manifolds? Do I use atlases or something else entirely?

Are chromatin remodeling complexes the same as histone tail modification?

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give the _rigorous_ definition of spin, please

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how much overlap is there between aerospace engineering and astrophysics?

please respond. please don't bully me.

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Yes.
Building planes and studying stars.
Only when you build planes that travel to space do they overlap.

>Only when you build planes that travel to space do they overlap.

what kind of overlap exists there? again, please no bullying.

How do I prove a group is closed under operation?

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>How do I prove a group is closed under operation?
Show that the composition of two elements under the operation is still an element of the group.

Any tips to memorize British and American unit system?
Inches, pounds, feet, Fahrenheit, pounds force, psi...
Come on

Also, what is the difference between lbf/in^2 and lbf/ft^2 ?

God, this is a mess

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Where can I read upon how electricity works?
Im trying to understand the basics so later I can understand how x-rays are created.

I am not native English speaker.
Youtube videos with Wikipedia definitions or flat out half assed explanations go over my head.
I need the basics explained like what is Volt,Amp ect. in a mater that is concise and understandable,and there is a concrete industry standardized in the terms used in the explanation since again I am not native English person and a lot of analogue terms make me even more confused.

Really stupid one.

Let's say we have a RLC circuit.
There is XL XC and R.
How would you word the difference between XL and R ? In some cases when I read "the resistance of coild is...." it's actually R not XL
So how do I differentiate between those two in text?
Also how is it with capacitor? How is the wording there?

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The group is a set with multiplication
weither an element is in the set depends on some property.
you show that this property holds for the product of two elements from the set.

If you know its a group then its closed under the group operation by definition.

If there is very little matter in the space, wouldnt the fact of "0 kelvin temperature" be irrelevant? In other words, wouldnt a body thrown into open space keep its internal temperature almost indefinitely, with no or very little particles to transfer heat to?

same user as I study electrical engineering so I should be able to do this.

I'll keep it simple like they did in my school because I am not quantum physicist.

Current is ordered flow of electrons and it's unit is A or "Amp"
I'll use our favourite water analogy DC is just like water flow but with electrons.
AC is electron going back and forth the higher the frequency the faster they go back and forth.

voltage unit V or "volt"
To this day I can't imagine it so I'll give you an analogy. imagine spring between each electron the more compressed the spring is the higher repel force between the electrons.
I gave up on imagining voltage I look at it this way
You can't have current without voltage so in your wall socket there is voltage between the two holes. Let's say it's "energy" between those two points, the higher the energy the further the electrons can go.
Also the definition of voltage itself is difference between two points. You can't have voltage in one point you always measure two.
So let's say it's "pressure" between those two electrons. The higher it is the more they repel the further they go.
I am not going to start with speed that's a rabbit hole.

Resistance unit Ω or "ohm"
The definition they told me is "the flow of particles with opposite charges in opposite direction as current" Think about resistance as the measure of the difficulty to pass for current.
Everything has resistance even the cable itself.
Without resistance you can have current in closed circuit theoretically forever. This is done with extreme cold it's used in CT machines.
The heat electricity produces is resistance as well.

So which way does current flows? Another good question. The answer is both directions.
Because flow of positive charges is electricity as well. But we say from + to - because that's the flow of positive chargers - is the flow of electrons.
Another important thing:
Current wont flow if your circuit isn't closed. That's how switch works.

Alright that is more understandable than 90% of the shit ive read so far.
Thank man.

my keyboard is failing so pardon my grammatical errors.

Only if that body can withstand the vacuum pressure

Okay, so temperature is not a concern but the pressure is, since said body will "want" to reach the same level of pressure around it(?). Thanks!

Retard here, trying to comprehend vectors
I'm supposed to calculate the distance between Q and the plain and realize that it's 0, meaing Q is on the plain

Besides what's on the drawing the task gives me the normal unit vector for the plain, called n
If I go Q - P0 to get the distance (I'll call it s, it's a vector) and scarlarly multiplay s with n the result is 0, so s and n are orthogonal

Is that proof of the distance between Q and the plain being 0?

There's an earlier example in my book where they calculate the shortest distance between the point and a line, the book says to look at that for help
In that task they calculate the distance s between the points Q and P0 like I did, but then they project it down onto the line, calculate another vector d from the tip of that projection back to Q, and the magnitude of that vector d is the shortest distance. Makes sense.
The difference here being that the point is away from the line and it's a line instead of a plain

Now if I try and project s down in my plain task the result is 0 because of orthogonal memery, meaning d is s, s has a magnitude meaning there would be a distance
I'm just supposed to get to where shit is orthogonal and quit, right?

I'm a total brainlet, with math I need someone to show me the exact task with different numbers so I can go "ah yes I understand what is being done here and why", I have massive trouble making any sort of connections on my own
Sorry for the drawing I'm on my mom's laptop and there's no mouse

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Is there a better drawing?

No, that's what I have to work with. I didn't leave anything out
Only thing I maybe should have made clear is that P0, e1 and e2 is what makes the plain, the plain E is P0 + variable1 * e1 + variable2 * e2
They give me all those vectors, but P0 seems to be the only useful one outside of maybe calculating a normal vector for the plain but they gave me that

forget it exists and use metric

why are low test soy asians so good at science? is soy the secret to science?

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>Is that proof of the distance between Q and the plain being 0?
Yes
>Now if I try and project s down in my plain task the result is 0 because of orthogonal memery
s is parallel to the plane, so the component of s along the normal vector to the plane is 0.
>s has a magnitude meaning there would be a distance
A non-zero distance between Q and P0, not between Q and the plane.

>s is parallel to the plane, so the component of s along the normal vector to the plane is 0.
Very helpful, I sort of couldn't put that together but now that you said it it really makes a lot of sense
Thanks user!

what is it called when you "cut up" regions in complex analysis?
for example when proving the residue theorem you can cut up the region as in the two pictures and prove it both ways.
i've heard the word surgery used, but im not sure if that's right

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How the fuck do you learn chemistry?
Math and physics are easy because advanced concepts are built on easy to understand concepts, but chemistry is the opposite because you have to accept that "it just werks".

There's no standard term for this. You would just describe choosing two different paths of integration

It would cool by radiation only. For a warm-blooded creature (e.g. human), that's nowhere near enough to get rid of body heat, so without some form of active cooling you'd die from overheating.

The temperature of space refers to the equilibrium temperature for an inanimate object which isn't generating heat internally. I.e. the temperature at which absorbed radiation equals emitted radiation.

Why?
I've got
[eqn] \lim\limits_{x\to x_0}\dfrac{f(x)-f(x_0)}{x-x_0}=f'(x_0)\,; \\
\lim\limits_{x\to x_0}\dfrac{f(x)-f(x_0)-f'(x_0)(x-x_0)}{x-x_0}=0 [/eqn]
but i can't see where to go from there, and i feel like i'm missing the o() part.

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hoe does xlogx = xln(x)

>Why?
What do you mean? It is a definition.

>It is a definition.
i didnt know that. i guess i meant why are the two definitions equivalent then

Lbf/in^2 is the pressure exerted by 1 Lbf over a one inch by one inch area.
Lbf/ft^2 is the pressure exerted by 1 Lbf over a one foot by one foot area.
1 Lbf/in^2 is 144 greater than 1 Lbf/ft^2.

To memorize British and American units, just do some practice problems, make a conversion sheet. Comes with doing it a lot.

General chemistry or what?

In this universe, it seems that things do not occur in isolation. Bacteria, religiotards, dog shit, planets, galaxies. Find one of anything and you will likely find millions.
It is reasonable to infer from this that the big bang is likely to be one of many. If so, we would be surrounded in all directions by other universes. The gravity of this huge surrounding mass would explain the accelerating rate of expansion of our universe.
No?

not necessarily
en.wikipedia.org/wiki/Shell_theorem

While it might be true, it would mean a non-uniform acceleration meaning we could see different expansion rates in different directions. We couldn't see uniform acceleration in your scenario because of the shell theorem.

I'm currently reading through several tough textbooks.

Would my time be best spent narrowing it down to one, and focusing strictly on that? Currently I bounce daily between, primarily, Spivak's Calculus, Knuth's Cocnrete Mathematics and Hoffman and Kunze's Linear Algebra. When I get BTFO and depressed by any or all, I often peruse easier works like Book of Proof / How to Prove It, or supplementary stuff like Tao's or Landau's work in analysis, MIT's Math for CS lecture notes, etc.

Is my strat shit or bretty gud? Anecdotally, I've noticed leaving and coming back with a fresh perspective is incredibly helpful. But perhaps it's more efficient to focus on one work at a time with monk like focus?


Pic absolutely not related

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might be worth noting I don't strictly adhere to opening each one each day, I take it as it comes. Sometimes I'll be on one all week, other times I'll cycle each frequently in one day.

The o() means there's a function that goes to zero faster than [math]x-x_0[/math]. Basically [math]\lim_{x\to x_0}\frac{f(x)}{x-x_0}=0\Leftrightarrow f(x)\in o(x-x_0)[/math]. Let [math]g(x)=f(x)-f(x_0)-f'(x_0)(x-x_0)[/math], and the previous statement gives you [math]g(x)\in o(x-x_0)[/math]. Denote [math]y=f(x),y_0=f(x_0)[/math] to get [math]y-y_0=f'(x_0)(x-x_0)+g(x)[/math]. The [math]g[/math] is usually just denoted [math]o(x-x_0)[/math], since it's an insignificant function anyways. Same thing works backwards, so the definitions are equivalent.

I'm really stuck on Thevenin Equivalent circuits.

I know how to get the equivalent resistance; I simply short circuit voltage sources and "open" the circuit where I want to put the two terminals of my resulting circuit

What Im' really stuck on is doing the Thevenin-Equivalent voltage.

Here's my thought process for solving the circuit in pic related.
They ask me to use Thevenin to get the current going through the ten-ohm resistor.
To get the thevenin-equivalent voltage, I short-circuit the 6-volt source and have an open circuit at the ten-ohms.
Now, we have a 5,20 ohm resistors in parallel, giving us four ohms. We then have 4-5-15 resistors in series, so this gives us
[math] R_{th} = 24 \Omega [/math]

Solving for the thevenin voltage, we open the circuit at the ten-ohm resistor and keep the 6V Source.
We have four volts going through the 20 Ohm and the 5-15Ohm branches, which means we have three ohms going through the 15-ohm resistor.
The 15-ohm and 10-ohm resistors are in parallel, so [math] V_{TH} = 3V [/math]

Finding the current through the ten-ohm resistor is thus
[math]
I = \frac{V_{TH}}{R_TH + 10} = \frac{3 } {34} = 0.088 A
[/math]

But when I look at the answer, I get that the result is 0.192 A. Where am I going wrong? I'm assuming it's the thevenin voltage expressions, but I'm not sure.

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>we have a 5,20 ohm resistors in parallel, giving us four ohms
this is correct

>We then have 4-5-15 resistors in series
this is wrong look at it again

the thevenin voltage was calculated correctly, but don't ever say that you have voltage through, say voltage across

Thanks!
I just saw another proof in a video that went like
[math]\cdots\Longleftrightarrow g(x)(x-x_0)=f(x)-f(x_0)-f'(x_0)(x-x_0)\text{ and } \lim\limits_{x\to x_0}g(x)=0\\ \Longleftrightarrow f(x)-f(x_0)=f'(x_0)(x-x_0)+g(x)(x-x_0)\text{ and } \lim\limits_{x\to x_0}g(x)=0\\ \Longleftrightarrow y-y_0=f'(x_0)(x-x_0)+\mathcal{o}(x-x_0)[/math]
Though I guess they're both the same since, in a hand-wavy sort of way, if g(x) goes to zero faster than x-x0, then g(x)(x-x0) will too.

does anyone have a copy of rudins memoirs? "the way i see it"

>does anyone have a copy of rudins memoirs?
Rudin is a meme.

when finding the curvature of a vector function. I understand it to be (dT/ds)/(ds/dt). Since ds/dt represents the change of length over a instant in time, why is it that ds/dt isnt a constant value since at any given instant moment in time the length is always the same?
idk if im making sense hopefully u guys get my question

also, whats the reasoning for having unit tangent vectors instead of just tangent vectors

lads how do I show symmetry and transitivity of this relation

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What have you tried?

amazon.com/Way-Remember-History-Mathematics-V/dp/0821806335

a_r = v^2 / r_curvature

Jesus user why do you need so much MATH

Can I get a quick rundown on [math]\mathb{Z}_n[\math] and its properties under "addition"?

[math]\mathbb{Z}_n[/math]

Aye baby
en.wikipedia.org/wiki/Integer

Nothing there about the sets of integers mod n

Look I'll just post the question and hope that someone spoonfeeds me.
A line is defined as the equation ax + by + c = 0.
I already have the solution but not the procedure to getting to the solution, so if someone could explain it (perhaps step-by-step) I'd be eternally grateful

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You asked about the localization of [math]\mathbb{Z}[/math] at an integer [math]n[/math], not about "sets of integers mod n".
There seems to be a typo as [math]\mathbb{Z}_7[/math] is not a field.

First point gives [math]a0+b0+c=0\to c=0[/math]. Show [math]b\neq 0[/math] using the second point and get [math]kx+y=0[/math], where [math]k=b^{-1}a[/math]; note that a solution [math](a,b)[/math] is not unique since you can always multiply the equation. Plug in second point to get [math]k=-6[/math].
I'm pretty sure 7 is prime.

>I'm pretty sure 7 is prime.
Yes, and?

If I know g, how do I find f in [math]\nabla\times f = g[/math]. I’m talking about very simple cases like g=(2x,0,-2z). My lecturer seemed to find f easily, but I can’t think how to do it without looking at a load of PDEs
Symmetry’s easy. If a/b=2^k, with k in Z and a, b in N, then b/a=1/(a/b)=2^{-k}=2^k’, with k’ in Z and k’=-k. Hence, b~a. Transitivity isn’t much harder, basically start with a/c and show it’s of the form 2^k.

Integers mod [math]q[/math], where [math]q[/math] is a prime power, are finite fields.

Sorry, I worded that wrong. Integers mod [math]p[/math] for prime [math]p[/math] are finite fields and you can build fields for prime powers.

Any anons mind helping me with this transformation efficiency problem? I'm a bit of a brainlet and I'm stumped. All the examples I've seen/had were much simpler.

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Yes, and? That still doesn't make [math]\mathbb{Z}_7[/math] a field since the ideal consisting of all elements of the form [math]\frac{3n}{7^k}[/math] in it is neither 0 nor the whole ring.

What does the dz/dx mean here?

it makes sense to write df/dx, in which you differentiate the function f, with respect to x, but in the pic related example the solution doesn't make any sense to me, where does the z^2 in the next line come from?

Could someone please do the computation between the two first lines as detailed as possible, so i see what's being done.

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I don't see what you mean. The field [math]\mathbb Z_7=\mathbb Z/\langle 7\rangle[/math] is generated by the ideal [math]\langle 7\rangle[/math], which is maximal and therefore the quotient ring is a field.

>[math]\mathbb Z_7=\mathbb Z/\langle 7\rangle[/math]
This is false since every ideal in a field is either 0 or the entire field, which is not the case with the ideal in my previous post.

Aight lads, figured out my problem.

Anyone familiar with calculating transformation efficiencies of colonies? Just need a check before I submit it ;x

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[math]\mathbb Z[/math] is a ring, not a field. If you want to consider ideals over [math]\mathbb Z_7[/math], just note that it has a multiplicative group [math]\mathbb Z_7\setminus\{0\}[/math] and it follows that the ideal is either 0 or [math]\mathbb Z_7[/math].

you differentiate z with respect to x, but 2(x^2 + y^2) pops up in the denominator which is just z^2.
this whole solution is an extreme abuse of notation and you just need to deal with it until you take your differential geometry class or whatever.

Do I understand it right that if we define S as bunch of S1,S2,S3,Sn where T= dt*n then Sn will be V (velocity)?

Talking about linear constant speed motion

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[math]\mathbb{Z}_7[/math] is not a field since [math]\frac{3}{7}[/math] in [math]\mathbb{Z}_7[/math] is both non-zero and not a unit.
Assume it is zero, then [math]7^k \cdot 3 = 0[/math] in [math]\mathbb{Z}[/math] for some [math]k \in \mathbb{N}[/math]. Assume it is a unit, then the set consisting of elements of the form [math]\frac{3n}{7^k}[/math] is a prime ideal which contains a unit.

This isn't my field at all, but how come the efficiency is way over the 0-100 range?

There is no [math]7^{-1}[/math] in [math]\mathbb Z_7[/math] and neither is there 3/7. It's not required by field axioms either, since [math]7=0[/math].

I'm currently a first-year Electrical Engineering major. I want to get possibly get into AI and robotics and also possibly neuron-controlled prosthetic limbs.

What should I learn for each of the two if I want to be really good at that field?

I'd start with Iron man 1 and then work progressively through the series from there. Take note of what the main character does when he encounters a problem.

What's the best way to get captured by terrorists who want me to build missiles for them?

>There is no 7−1 in Z7
7 is trivially a power of 7 and is thus a unit in [math]\mathbb{Z}_7[/math].
>neither is there 3/7
What are you talking about? Is 3 not an integer?
> since 7=0.
Units cannot be nilpotent in a non-trivial ring.

given linear equation

x + y = 15

How do I properly write the range of all [math]\mathbb{N}[/math] numbers for x/y pairs which satisfy the equation?
It will be something like n-x + x i.e. 15-3 + 3

Find me an integer [math]n[/math] such that [math]7n=1 \mod 7[/math]. Clearly it doesn't exist, so 7 has no inverse.

seriously though. What should I learn? I'm kinda proficient in c++ and cad software but what should I know? What's the best way to learn about neural networks?

Yes, 7 is a nilpotent in [math]\mathbb{Z}/(7)[/math] and is thus not a unit. Your point?

Having trouble with the follow up too. (Sorry, supreme-brainlet here)
A line [math]r[/math],
[math]a_1x_1+b_1y_2+c_1=0[/math] is parallel to line [math]s[/math] : [math]a_2x_2+b_2x_2+c_2=0[/math] if no pair [math](x,y)[/math] satisfy both equations when plugged in.

I know there's such a line because from the axioms of affine space, for any two points P and Q there must be a line that passes through both.

Plugging in (0,1) and (1,0) into the general equation for a line implies that a_1 = b_1 = c_1, so my thinking is if I simply go through {1,2,3,4,5,6}

for (0,1) and a = 1, 1*0 + 1*1 + 1 = 2 != 0
for a = 2, 2*0+2*1+2=4 != 0
for a = 3, 3*0+3*1+3=6 != 0
for a = 4, 4*0+4*1+4=8=1 != 0
and so on, so no choice seems to make sense?

I wrote the stuff above for those who get angry at people who ask questions without putting any effort in, it's fine if you don't read it and just spoonfeed the answer. Thank in advance

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a-b=11
a+b=90
a,b=?

1) what is the equation of the line they are asking about, it would help to find that wouldn't it?
2) parallel lines have the same slope

is libgen illegal?
i wanna get about 100 files but will it set off alarms at my isp?

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b = - 11 + a
a+b = 90
a + (-11+a) = 90
2a = 90+11
2a = 101
a = 101/2

simple linear equation y = kx+m