/sqt/ - Stupid Question Thread

>is that for the one in brackets?
no, the one in brackets is -2/3

...

What is the simplest possible way to convert direct current into alternating current without ANY moving parts?

This question is really bothering me because all of modern civilization depends on the process but yet nowhere does it actually explain how its done. I am neither a physicist nor an electrical engineer, but I've been trying to teach myself and I think I have a good understanding of the basics.

i think im asking where we get the numbers to replace x

i got that part, im just unsure on how it goes from there to the next line

nvm i got it thanks. if i seem retarded its cause im teaching myself and it can be hard to grasp it all just by reading worksheets.

>unsure on how it goes from there to the next line
f(x) = x-(x^3)/3
b=1
a=-1

>convert direct current into alternating current without ANY moving parts
you can't do it, as far as I know

electroschematics.com/7032/12v-to-120v-voltage-inverter/
Depends if you want a specific waveform. That'll give a square wave.

Oxygen is produced from the bleach/peroxide reaction, hydrogen from the aluminum/acid reaction.
They mix together in the bottle. The fire triggers the reaction. Oxygen+hydrogen=water.

right
Bicarb soda + vinegar is always a hit.
idk, maybe make batteries? Work up from basic lemon batteries to electroplating and rare metal recovery.

Dude just fucking write it out next time. It's simple algebra at that point

Make an IED my dude

Can someone please explain the axiom of choice to me? As far as I know given sets A B and C it's possible to construct a set D that contains one element from each of them. Why wouldn't that be possible and why does AC imply you can somehow double objects?

Can you define a homomorphism from a group to another in this "cheaty" way?

Let [math]A,B[/math] sets and [math]A\coprod B[/math] their disjoint union. Let [math]F(Z)[/math] be the free group on the set [math]Z[/math]. Suppose there are homomorphisms [math]f_A: F(A)\to G[/math], and analogous for [math]B[/math], to a set [math]G[/math]. We have some natural injections [math]j_A:F(A)\to F(A\coprod B)[/math], analogous for [math]B[/math].

Can I define a homomorphism [math]\phi :F(A\coprod B)\to G[/math] by [eqn]\phi(x)=\phi\left(\prod_{g\;\mathrm{ a\;generator}} g^i\right):=\prod_{g\;\mathrm{ a\;generator}} \phi(g)^i[/eqn]

Define [eqn]\phi(g)=\begin{cases} f_A(g) & g\in A\\ f_B(g) & g\in B\end{cases}[/eqn]
Which obviously is a homomorphism by construction, and makes the diagram commute?

what's gonna happen on september 23rd

yes

Why do people tend to get worse hangovers as they get older? Something I hear from a lot of people: "I didn't get hangovers in college, but I started getting them in my mid 20s, and they kept getting worse". Why does this occur? I remember in college I would wake up after a night of heaving drinking feeling fresh as a daisy, but now, after a heavy night of drinking, I feel severely debilitated mentally and it takes me like a full 2-3 days to recover.

Is my this correct??

Use induction to show that n3-n+3 is divisible by 3 for all natural numbers n

P(1) —> 13-1=3 = 3 P(1) is divisible by 3

Assume P(k) is true

k3-k+3 is divisible by 3

Show P(k+1) is true

(k+1)3-(k+1)+3

= k3+3k3+2k+3

P(k+1) is true thus, for (n), all natural numbers are divisible by three

damn , messed yup the exponents

I dont' know anything about science so this question is very stupid: how would a scientist actually "see" my genetics, or DNA? Would they have to take a piece of my body (skin, hair or such), place it under a microscope? Can they actually see, with their own eyes, what my genes look like?

Hi guys I started learning linear algebra last week and I'm stuck on a part of a problem here.
Let T be in Hom V and nilpotent so that T^n=0, but T^(n-1) =/=0 and assume V has the property that any of its subspaces has a complement (in terms of direct sum to V). That is for any subspace M in V, there is a subspace N with M and N forming a direct sum for V.
Now let V_1 be the complement of the null space of T^(n-1) called N^(n-1) here. I have shown that the intersection of T[V_1] and N^(n-2), the nullspace of T^(n-2), only contains the 0 element. I have also shown that T[V_1] is a subset of N^(n-1).
The part I'm stuck on is asserting the existence of a subspace V_2 such that V_2 and N^(n-2) form a direct sum for N^(n-1) but T[V_1] is a subset of V_2.

No. [math] \phi [/math] can give different values for different presentations of the free groups. It is not well-defined.

what is the step that is incorrect then?

How else would you show that [math]F(A\amalg B)=F(A)\ast F(B)[/math]?

[eqn](n+1)^3-(n+1)+3=n^3+3n^2+3n+1-n-1=(n^3-n+3)+3(n^2+n)[/eqn] and it is divisible by [math]3[/math] by induction hyp.

Suppose that [math] gcd(m,n) = 1 [/math]

How do I prove that [math] gcd(m^2 - n^2,mn) = 1 [/math] and [math] gcd(m^2 + n^2,mn) = 1 [/math] ?

ill post the answer after this hint:

Let [math]d=gcd(m^2-n^2,mn)[/math]. Now show [math]d=1[/math]

How many hours a day would I have of classes (assuming 5 days with classes per week) if I had set myself the goal of a BA with a double minor in 4 years? What if it was a triple minor?

I'm an illustrator, and I need a little help understanding a positive control test for a comic I'm doing in which the script has some sciency jargon.

Is a positive control test basically just a way to compare something you expect to happen against whatever you're testing if a variable in the positive control is removed or nonexistent?

Say you were testing a bullet-proof vest against an older version of said bullet-proof vest. Is that considered a positive control experiment?

Let [math]d=gcd (m^2-n^2,mn)[/math]. Then in particular, [math]d|mn\implies d[/math] divides exactly one of [math]m[/math] or [math]n[/math] by the condition [math]gcd(m,n)=1[/math]. Then assume without loss of generality that [math]d|m[/math]. So we can write [math]m=kd[/math] for some integer [math]k[/math].

Now we also have [math]d|m^2-n^2=k^2d^2-n^2[/math]. So we have to have that [math]d|n^2\implies d|n[/math]. But since [math]gcd(m,n)=1[/math], then [math]d=1[/math]

How do you get from "Since ..." to "we see that ..."?

September was last year, my dude

Best way to find top professors in a given field? Just searching google scholars? Will top unis always have top professors aswell?

given its a finite field just look for the one with the highest characteristic

>. Then in particular, d|mn⟹dd|mn⟹d divides exactly one of m or n by the condition gcd(m,n)=1

What, why? What if d is equal to mn. Then d does not divide either.

Think of d,m and n in terms of their decomposition into prime numbers. If d divides a bit of m and a bit of n, then that means that gcd(m,n) is at least d>1. Contradiction

You use the given identity to get to an equivalent expression and then you use the triangle inequality.

Wait, I think I can formalize your idea. I can say [math] d = d_1 d_2 [/math] where [math]d_1 [/math] is the biggest divisor of d that also divides m (but not n), and [math]d_2[/math] is the biggest divisor of d that also divides n (and not m).

Then using your method I can prove [math]d_1 = 1 [/math] and [math] d_2 = 1 [/math] and therefore [math] d = 1 \times 1 = 1 [/math].

>. If d divides a bit of m and a bit of n
I am saying in the case that d does not divide either m or n, which is possible if you only know that d is a divisor of mn. Like in the case d=mn

>what is the step that is incorrect then?
Attempting to define the homomorphism by its action on the elements. Essentially, you're passing the construction through a functor [math] \textbf{Grp} \rightarrow \textbf{Set} [/math], which is forgetful, and pretending that this never happened. You no longer have the group structure, it went poof through the functor.
>How else would you show that...
You can't. They're isomorphic, not equal. Equality only holds if you define the free group by a universal property, i.e. by a functor [math] \textbf{Set} \rightarrow \textbf{Grp} [/math] (so you essentially don't care about the underlying set any more).

Of course, you should be able to produce a formal proof, but I'm assuming it's your first time with these arguments, because that is wrong.

Suppose the [math]d_i,m_i,n_i[/math] are primes, and that [eqn]d=d_1^{\alpha_1}\cdot d_2^{\alpha_2}\cdot...\cdot d_{k}^{\alpha_k},\; m=m_1^{\beta_1}\cdot m_2^{\beta_2}\cdot...\cdot m_{h}^{\beta_h},\;n=n_1^{\gamma_1}\cdot n_2^{\gamma_2}\cdot...\cdot n_{j}^{\gamma_j}[/eqn]
This is obviously very cluttered already, but what it means is that you can decompose [math]d,m,n[/math] in to products of prime powers.

You have that [math]d|mn[/math]. This means that there is some integer [math]a[/math] such that [math]da=mn[/math]. Now write out what this means:

[eqn]ad=mn\iff a\cdot d_1^{\alpha_1}\cdot d_2^{\alpha_2}\cdot...\cdot d_{k}^{\alpha_k}=m_1^{\beta_1}\cdot m_2^{\beta_2}\cdot...\cdot m_{h}^{\beta_h}\cdot n_1^{\gamma_1}\cdot n_2^{\gamma_2}\cdot...\cdot n_{j}^{\gamma_j}[/eqn]
Since you can decompose every integer into prime powers uniquely, this means that you can mix and match [math]a[/math] and the [math]d_i[/math] with [math]m_i,n_i[/math]. But [math]gcd(m,n)=1[/math] means that none of the primes are shared between m and n. But now you think, yes, but what if d has some primes that divide m, and some that divide n? Well, if that were the case, then those primes would divide both m and n. But this is not possible because their gcd is 1

well, how do you show they're isomorphic then? I'm assuming it's a typo in the book

I think you.re being trolled. The construction in your first post was fine. Also saying "equal" instead of "isomorphic" is common practice and not such a big deal

i'm curious about growing crystals or making synthetic stones. there are a bunch of "grow crystals at home" projects using alum and copper sulfate etc, but apparently the resulting crystals are quite fragile.

i want to make crystals/stones that are about as durable as decorative natural crystals/stones, such as amethyst or just a plain normal stone.

do you know what types of crystal/stone and the method of synthesizing them would be worth looking into? if it requires using equipment like a pressure cooker or an autoclave or exotic chemicals i'm still curious about it.

>saying "equal" instead of "isomorphic" is common practice
In category theory.
>The construction in your first post was fine.
Except it wasn't.

How do you guys maintain motivation and focus to study? I'm struggling right now to study mathematics :/.

I think you've got it. It just means that, if your experiment is set up correctly, you will see x result with y control since you already know that y control gives x result under the right conditions. Say if I were testing the pH of some substance, a positive control would be when I test a known acid or base to make sure I get that result. You probably could have just googled this though

Are blacks (on average - and that's an important word) genetically less intelligent?

I think they are.

yes

can I use binomial theorem in place of pagels triangle in any problem that calls for expansion?

hey i fucked up and need to learn stoichometry, termochemistry, kinetics, and daniel pill untill tuesday
is it possible or should i just give up and try general chemistry for the 3rd time?

I think that's right. Which is why we need to seriously reconsider "diversity" policies.

>genetically
Do you mean do they genetically have a lower capacity for intelligence? If so, there is no definitive proof. Yes they do have a lower average IQ, but whether that it is caused by a lower capacity for intelligence genetically or a lack of quality education is unknowable, because the only way to really know that is to give them quality education.

Can anyone help me understand how time spent in college works? I've never been to college before. From what I read, its way less time than school (18-20 hours a week as opposed to 30-40). Is there an option to go to college for 7 hours a day, but only 3 times a week? Or do you have to spread the hours over the five weekdays?

So it's been a while now

I don't want to make a thread about this

Has the discovery of the Higgs boson yielded any new shit that's interesting or useful to humans?

No. Most of these discoveries don't mean much to the average person, but at least it's still better than investing the same money in wars.

Gonna soon go through a government clearance for an internship which will probably lead to a job. I'm 23 and live in the state of California, when I was 20 I got my medical marijuana prescription, kinda on a whim with my buddy cause it took 30 mins. I plan on telling them this, but do you think there's a chance that it could give me problems with passing? Rest of my file is clean

[math]13-.5w+6x; w=10, y=\frac{1}{2}[/math]
why is the answer not 5

fuck, I figured it out
[math]13-5+3[/math]
I keep on getting questions wrong on khan academy because I've always been taught Multiplication gets priority over Division, Addition gets priority over Subtraction a la PEMDAS

what the fuck is the truth?

13-5+3

Hmm rly makes me think

see
I was always taught that you always do addition before subtraction, not that they have equal priority and to go from left to right through the equation

It's more like PE(MD)(AS)

Multiplication/division and addition/subtraction have equal priority

>I keep on getting questions wrong on khan academy because I've always been taught Multiplication gets priority over Division, Addition gets priority over Subtraction a la PEMDAS
fucking burgersharts lmao

my math education was so poor that I'm now trying to re-teach myself basic algebra so I don't blow it when I start college

What are some good books or resources for learning notation?

Is there any simple way to prove that the diophantine equation [math] x^4 + 4y^4 = z^2 [/math] has no all-positive solutions?

Can anyone recommend a chemistry textbook for someone who failed high school chemistry, mostly for not doing any work, but who enjoyed it none the less?

How many hours of classes a week would I need to get the following in 4 years:
-1 major 1 minor
-1 major 2 minors
-1 major 3 minors
-2 majors 1 minor
-2 majors 2 minors

Have we found anything smaller than quarks yet?

Would it be a good idea to put little windmills on top of those really tall power lines? That way we don't have to build that whole big windmill thing and it saves money right?

Fields.

We have a deck of 25 cards with 2 jokers in there, we draw 10 cards, and we can shuffle 1 back 3 times, a card we've choose to shuffle back cant be re-drawn. What are our chances of having 1, or the 2 jokers amoung our 10 cards after the shuffling?

Nearly every electronic device you interact with every day relies on the creation of an alternating electric potential, in some way. Smartphones are powered by a DC battery and can generate signals at 5 billion hertz. How does THAT happen?

From my understanding, the voltage on the gate of each resistor will always be the same, even if the resistors are open, so both will be held open constantly. I can't see how this would alternate.

>Nearly every electronic device you interact with every day relies on the creation of an alternating electric potential, in some way.
And mechanical switches haven't been used in over 50 years.
>resistors
I meant transistors.

Shut it, brainlet, yeah? We power engineers don't need advice from you. If it was that easy we'd have done it already. Or maybe you think there's some conspiracy "keepin' duh white man down"?

is the derivative and integral of e^-x = e^-x like how e^x = e^x?

No, use the chain rule.

d/dx e^-x = -e^-x

cool thanks

I don't know if I should do EE or CS yet, fuck.
I also have the chance to study in a top 4 uni in Japan (I'm here right now preparing for entrance to uni but I still can't decide my major, I have 3 months left, can anyone give me some advice?(

I only did basic calculus in school but I remember using the power rule and other formulas. I've opened Keisler Calculus and I'm being bombarded by infinitesimals and standard parts. I have no idea what these are.

Why is the voltage across C1 is 0?

If I have a cube in a vacuum and there's gas inside the cube that produces a pressure of 10 Pa, will then the force that the pressure exerts on each side of the cube be 10/6N?

You have symmetry. C2 = C4 and C3 = C5, so the voltage across C1 must be symmetric: V1 = -V1 => V1 = 0.

What if the capacitors aren't symmetrical?

Then you have to calculate.

How do I do it? Make equation from each loop using V=Q/C?

Deck is 16 red, 16 black
"How many results are there to draw 3 cards with exactly 1 red card"

do i have to add or multiply the C ?

Multiply,since you are drawing 1 red AND 2 black.

thanks

How bad is direct skin contact with 95% ethanol?

Just spilled a bunch on my bench and some got on my arm.

Each loop and each junction. Kirchhoff's laws but with charge instead of current.

It's literally alcohol. You can literally drink it.