/sqt/ - Stupid Questions Thread

If IQ is hereditary and individuals lose IQ over time does your offspring end up more intelligent if you have them when you're younger?

>his testosterone-ridden masculine body "conquered" hers?
Kill yourself

Can I calculate the limit of a multivar function in a point where the function is not defined in a direction?

> Can I calculate the limit of a multivar function in a point where the function is not defined in a direction?
No, the limit definition requires the function be defined in some neighbourhood around the point

That's what i thought, but the thing is the limit seems to be possible to calculate.
It's the limit of sin(x*y)/y as as (x,y) approaches (0,0)
If you do lim sin(xy)/y = lim x/x * sin(xy)/y = lim sin(xy)/yx * lim x = 1 * 0 = 0

>If you do lim sin(xy)/y = lim x/x * sin(xy)/y = lim sin(xy)/yx * lim x = 1 * 0 = 0
Doesn't tell you about approaching from x-axis.

Could someone check my answers:
Force from BC is 230.69 pounds
Force from AC is 172.73 pounds
sorry I'm a brainlet

Here's a good one, how do fucking electrodes work? I have a cathode and an anode as stimulation electrodes and another two for recording the signal. How do I position those, why do I even need two of each? I'm supposed to be measuring action potentials.

Yes, but not for the reason you think.

Losing IQ as you age doesn't actually change your genes, so your offspring wouldn't end up more intelligent if you have them younger, however, having children too late can actually lead to less intelligent children, among other problems associated with having children late in life, although it's mostly a concern with an older mother rather than an older father.

>having children too late can actually lead to less intelligent children, among other problems associated with having children late in life, although it's mostly a concern with an older mother rather than an older father.
I know this is a thing for women because down syndrome rates start to skyrocket but are there any standout issues for men?

Would multiplication in the visualization of dots in rows & columns for something like 3*8 be stated as three rows & eight columns, or three columns & eight rows?

Does it even fuckin matter? I don't know, I'm fucking terrible at mental math and I'm trying to just start back at ground zero by using mental visualizations & then manipulating those visualizations in order to complete the mental math.

>Does it even fuckin matter?
no

3*8 = 8*3. So even if it mattered it wouldn't matter.

Until you get to Matrices. Fucking Matrices.

If all false statements became true and vice versa, would the resulting system be consistent?

Can we use Quantum Entanglement to create some form of instant communication? If two particles can perform the same/inverse functions at any (virtually infinite) distance, can't we build two rings that hold quantum entangled particles and then use those particles to read off a Hexadecimal language?

Assume I know next to nothing about Quantum Entanglement (but can understand that math of it all), what am I getting wrong here? Or if I'm not, why aren't we looking into it?

In the solution he didn't consider the atmospheric pressure. Can someone explain me why?

Nevermind, I didn't read the question properly.

Only extremely fringe interpretations of Quantum Entanglement claim that the quantum particles are actually in communication with each other and among them an even smaller fringe states that that communication will continue if either particle is altered in any way.

It's more like a particle will decay into two particles in two different directions and if you learn something about one particle it will tell you something about the other no matter how far away it is. It's just really weird on paper because technically the other particle should still be relying on the fact that it's unknowable. Though I'm not going to pretend I know the mathematical ins and outs.

Even if you don't know the mathematic magic, what you said actually makes a lot more sense and now is making me wonder, "Why the fuck is there any hype about Quantum Entanglement anyways?" I realise I definitely had a misinterpretation of how this worked. There's a reason why I dropped this in the /sqt/, thanks user.

>Why the fuck is there any hype about Quantum Entanglement anyways?
Because those fringe interpretations DO exist and they sell journals and inspire science fiction stories, so they're more popular than the more subtle interpretations.

>Or should I just go check it's algebraic properties?
Let's start with that.

What's a good template for making (personal) notes in latex?

the criteria for this question in pic related seems a bit vague to me. anyone have a clue?

ah shit wrong pic. check this one. what do they mean by "simpler function?"

Nevermind. Much easier than I had thought.

How did we transition from 2Re(z*w*) to 2|zw| in the 4th step?
Taking real analysis and so far everything seems alright though I can't understand all definitions from the first time.

Re(a)

is this u?

It's wrong. Should be 2 Re( zbar w )

Why do people say stock prices are perfect when there are obvious price fluctuations over nonsense?

Do stock prices ultimately correct or what?

Why is it when I am drinking mineral water it doesn't feel that heavy compared to tap water?
Is it pH levels or is it something else to it.

Yeah my bad

Are peeps still here? Dumb-bum reporting in.
What, if any, is the name for the lower leg? From the knee to the ankle (circled in blue)

crus or cnemis
In common folk term, the front is called shin the rear is called calf.

Thank you for the specificity; that did not help me figure out my confusion though. I will try again with more information.
As 'foreleg' is not a common term used in describing human legs.... I am having no success on Google.

" the disproportion in my build is that my forelegs are too short. Like the kangaroo, I have very short forelegs and tremendously long hind legs. Ordinarily I sit quite still; but if I move, the tremendous leap that follows strikes terror in all to whom I am bound by the tender ties of kinship and friendship."

I am having trouble understanding if the author means the 'foreleg' as the half of his leg above or below the knee?????

That describes front and rear legs.

>Why do people say stock prices are perfect when there are obvious price fluctuations over nonsense?
Shouldn't you be asking those people that question?

This one had me kinda stumped (yes, I'm dumb).
[math] \lim_{x\to0}x^2=0 [/math]
Given [math] \epsilon \gt 0[/math] we wish to find [math]\delta [/math] such that:
[math] 0 \lt |x| \lt \delta \Rightarrow |x^2| \lt \epsilon [/math]
[math] \Rightarrow |x||x| \lt \epsilon [/math]
s.4cdn.org/image/buttons/burichan/cross.png
Is delta supposed to be epsilon over x or equal to delta? The former makes no sense, the latter I'm skeptical of. Maybe 2 times epsilon?

I'm a complete brainlet but isn't delta just sqrt(e)?

You're probably right.
[math] |x^2| \lt \epsilon [/math]
[math] |x| \lt \sqrt{ \epsilon } [/math]

Not sure if you can square root... well.
[math] |x^2| = |x|^2 [/math]

So [math] \delta = sqrt{ \epislon } \Rightarrow |x^2| = |x|^2 \lt \delta^2 = (sqrt{ \epsilon })^2 = \epsilon [/math]

Is that it?

That's what I was thinking, yeah. Why wouldn't you be allowed to square root here? Nothing here that would exclude that. Also no funny business with negative roots since we have absolute values. But then again, I'm a pretty big brainlet so don't trust me.

I remember the wiki having recommendations books for html5 and I can't find them now, was that section deleted or I'm just imaging things and it never existed at all?

What's the best youtube lecture series for ODE?

The square is a monotone function on either side of 0, so let f(x)=x^2, then 0

d/dx ((x^3)/(f(x)))
at point x=4 and where f(4)=1 and f'(4)=2

please tell me the answer is -20

Nope, sorry.

what is it then

MIT lectures are decent:
ocw.mit.edu/courses/mathematics/18-03-differential-equations-spring-2010/video-lectures/

Just use the quotient rule and plug in the numbers. It's not that hard.

did that and got -20, but the answer was wrong and i can't see where i fucked up

figured it out now

You probably divided by the wrong number. You said yourself that f(4)=1, so you need to divide by 1^2=1.

Just started Partial Diff Eq, can anyone help me with this problem?

For the Hydrogen atom, if [math] \int |u|^{2} dx = 1 [/math] at [math] t=0 [/math] show that the same is true at latter times. (Hint: Differentiate the integral with respect to t, taking care about the solution being complex valued. Assume that [math] u [/math] and [math] \bigtriangledown u \rightarrow 0 [/math] fast enough as [math] |x| \rightarrow \infty [/math] ).

math.stackexchange.com/questions/189809/hydrogen-atom-in-partial-differential-equations
Literally the first google result.

What is the probability of randomly choosing a permutation of the 10 digits 0, 1, 2, ..., 9 in which 5 is not in the first position and 9 is not in the last position?

A: {(1×9×8!)+(8×8×8!)}/10!

Wtf, why? My idea was to calculate all the permutation and subtract out ones starting with 5 and ending with 9.

( 10! - 8! ) / 10!

Why is this not right? And why is what is right right? fuck nigga

>Just started Partial Diff Eq, can anyone help me with this problem?
differentiate as the hint says. use the schroedinger equation et voila

Hey people, i'm stuck with these two :

"Consider the differential equation [math]\ddot{x}
= \sqrt{x} [/math], with initial condition [math]x(0) = \dot{x}(0) = 0 [/math]. Is the solution unique ? If not why is the exemple pathological ?"

and

"Is it true that a once differentiable function [math] x(t) [/math] is a solution of [eqn]m\ddot{x} = -ax [/eqn]
ifand only if it is a solution of [eqn]\dot{x} =
\frac{2E}{m} - \frac{a}{m} x^2 [/eqn]? If not, find a non trivial counterexemple."

So it's classical mechanics but I must admit my math skills are rusty, I suppose that I obviously don't have to solve the nonlinear ode-s in order to answer the questions. But I've forgot how one can prove the existence/uniqueness of a solution of ode aswell as that it's a pathological solution.
Can someone help me to get on the tracks pls ?

Why is the Earth's core still so hot? I read its still the approximate temperature of the surface of the sun and is supposed to remain so for billions of years., it'll be hot and liquid long after the sun converts to a red giant, for example.

Seems like an improbable thermal flywheel to retain such heat energy for so long. Why does it take so long to dissipate when most rocky objects around are at such lower energy states throught?

Could anyone help me finish up a proof I'm working on? Or suggest a different approach to proving it?

"Prove that if [math]a \equiv b (mod n)[/math], then [math]a[/math] and [math]b[/math] have the same remainder when divided by [math]n[/math]."

Here's what I've got so far:

Suppose [math]a \equiv b (mod n).[/math] Then [math]n | (a - b)[/math] and [math]a -
b = nk, k \in \z[/math].

Let [math]a = qn + r, 0 \leq r < n[/math] and [math]b = pn + t, 0 \leq t < n[/math]. Thus
[math][(pn + r) - (qn + t)] = nk[/math]
[math]r - t = n(k - p + q)[/math].

Since [math](k - p + q) \in \z[/math] we have that [math]n | (r - t)[/math] or in other words [math]r \equiv t (mod n)[/math].

After that I'm stuck. Intuitively I "know" that since neither r nor t are divisible by n them being congruent to each other mod n means that they must equal each other, but I'm not sure how to actually show that. The proof in general also seems a bit long for something so simple.

Is stating "Q is a necessary condition for P" synonymous with the contrapositive of P -> Q?

Could anyone help me finish up a proof I'm working on? Or suggest a different approach to proving it?

"Prove that if [math]a \equiv b (mod~n)[/math], then [math]a[/math] and [math]b[/math] have the same remainder when divided by [math]n[/math]."

Here's what I've got so far:

Suppose [math]a \equiv b (mod~n).[/math] Then [math]n | (a - b)[/math] and [math]a -
b = nk, k \in \mathbb{Z}[/math].

Let [math]a = qn + r, 0 \leq r < n[/math] and [math]b = pn + t, 0 \leq t < n[/math]. Thus
[math][(pn + r) - (qn + t)] = nk[/math]
[math]r - t = n(k - p + q)[/math].

Since [math](k - p + q) \in \mathbb{Z}[/math] we have that [math]n | (r - t)[/math] or in other words [math]r \equiv t (mod~n)[/math].

After that I'm stuck. Intuitively I "know" that since neither r nor t are divisible by n them being congruent to each other mod n means that they must equal each other, but I'm not sure how to actually show that. The proof in general also seems a bit long for something so simple.

Repost to fix the latex.

Yes, but it's also synonymous with P -> Q.

Right, whereas the "sufficient condition" only refers to [math]P \rightarrow Q [/math] and not [math] \neg Q \rightarrow \neg P[/math], correct?

No, for two reasons. P -> Q is synonymous with ~Q -> ~P, and saying "Q is a sufficient condition for P" means Q -> P.

Your whole proof is shit and you've basically ended up back where you started.

That said, use the fact that both r and t are between 0 and n to conclude that they are equal.

Ah, okay, was confused on the grammar of the statements, that's fairly straightforward then.

I actually don't end up where I started, and I figured out how to end my proof (even if the proof is admittedly, shit).

[math](1) r - t = n(k - p + q) = ns, s \in \mathbb{Z}[/math] and [math]0 \leq (r - t) < n[/math]
[math]0 \leq \frac{r - t}{n} < 1[/math]. Since [math]\frac{r - t}{n}[/math] is an integer from (1) we conclude that [math]r - t = 0[/math] and [math]r = t[/math].

It's still an ugly proof, I agree, and I'd love to see your take on it.

My take on it: a-b has remainder 0

nuclear detonations in atmosphere or solar flares:
will disconnected hard drives and electronics survive fine?
what about hard drive in ESD-bags?
ESD-bags wrapped in aluminium foil?

electromagnetism is not one of my stronger topics

Ah, OK. I feel stupid now. So how about this?

Suppose [math]a \equiv b (mod~n)[/math]. Then [math]n | (a - b)[/math] which means that [math]a - b = nk, k \in \mathbb{Z}[/math].

Let [math]a = qn + r, 0 \leq r < n[/math] and let [math]b = pn + t, 0 \ leq t < n[/math]. Then [math]pn + r - qn - t = (p-q)n + (r-t) = kn[/math]. Since [math](r - t) < n[/math] we have that [math]p - q = k[/math] and thus [math]r - t =
0[/math] and [math]r = t[/math].

Was that better? Could you simplify it even further without losing formality?

Mixed up p and q there, but you get what I mean.

I want to know how I can concentrate muriatic acid from the 31% jugs to as concentrated as possible. Can I just boil off the other liquid that comes in the jug.

>I want to know how I can concentrate muriatic acid from the 31% jugs to as concentrated as possible
Hydrochloric acid has a maximum concentration in solution of about 38%. You can't concentrate it further than what you can buy at the store, boiling it is just going to cause poisonous vapors.

"As concentrated as possible" is ~42% at 20C. It's rarely made above 35% because the evaporation rate increases dramatically as you approach saturation.

Heating it will reduce the concentration: the boiling point of HCl is -85C, versus 0C for water.

> versus 0C for water
Um ....

>Heating it will reduce the concentration: the boiling point of HCl is -85C, versus 0C for water.

>Heating it will reduce the concentration: the boiling point of HCl is -85C, versus 0C for water.

And to think I had shame to ask my stupid question.

A number x is in the subset of Reals which is (0, 1). How do I construct another number in the set smaller than it? I want to do 1/x but that makes it > 1...

Is there anything that will take away the overwhelming desire to not exist?

Have you tried the double chalupa?

No

Maybe reading some books by Jean-Paul Sartre?

>How do I construct another number in the set smaller than it?
just think about it...

Sure, recommend one?

x / 2, I'm dumb

"Being and Nothingness" is supposedly his seminal work. Never read it myself though.

Link to the pdf
libgen.pw/download.php?id=360461

Sorry, that's a link to class notes about the book. Here's the actual book.

libgen.pw/download.php?id=531452

well there's your problem

How far away are we from creating the virus that only kills all white people?

Thanks user, I'll check it out

Somehow I don't think a fried tortilla filled with meat and cheese will help. Chalupas worked when I was younger but now I just hate myself after eating that stuff