SQT - Stupid questions thread.

[Anonymous No.9290753]

Stupid questions thread, since there is no current thread.

Assuming a TV has been exposed to rain for a limited time, and there are some water droplets inside, how long should it take for them to completely evaporate, assuming the TV is being stored in a wind-still room with a temperature of 15-20c?

[Anonymous No.9290769]

>>9290753
What's the humidity in the room?

[Anonymous No.9290779]

>>9290753
there's a hundred different variables. Either way though, you don't want to let it evaporate unless you are comfortable replacing the capacitors yourself.

[Anonymous No.9290785]

>>9290779
What do you mean? How does evaporating water damage capacitors?

[Anonymous No.9290789]

>>9290769
>>9290779
Not sure about the humidity, probably the average for indoors. It's not like I'm interested in the exact minutes, I just need an answer with a margin of error of like +- 1 day.

[Anonymous No.9290796]

>>9290753
>droplets

When will they learn?

[Anonymous No.9290812]

>>9290785
the water/humidity does. If you wait til the water evaporates they will almost surely be trash. If you dry it quickly, you might get lucky.
>>9290789
there's no way to tell, even with large margins. Water could have collected in some area which would not evaporate any time soon since it not just a wet part. You could expect most of the tv to be dry in a week, but that area could hold water for a lot longer so when you turn it on you'll still fry something.

[Anonymous No.9290825]

>>9290812
>the water/humidity does
But how exactly? The TV was only exposed for a limited time, I'm not even sure if any droplets got inside. If they did, they might not even be near any capacitors. I don't see how the humidity increase from a couple drops of water inside could destroy capacitors.

[Anonymous No.9291119]

There is a question in Rudin's book that develops the recursive formula [math]x_{n+1} = \frac{\alpha+x_n}{1+x_n}[/math] for approximating square roots.

Is there a good explanation of what this method is actually doing (like how the Babylonian method has a sensible reason) or is this just another one of Rudin's asspulls?

[Anonymous No.9291129]

Didn't get my answer from the last thread in part c I am getting different answers for the power energy time and the acceleration velocity time.


ai) [math]F=m\cdot a[/math] so [math]a=\frac{F}{m}[/math] which ends up giving me an acceleration of [math]\frac{4}{3}ms^{-2}[/math]
Then [math]W=F\cdot s[/math] which gives work as 96.0J
ii) so assuming that W=E here its going to be [math]v=\sqrt{\frac{2W}{m}}[/math] which gives a speed of [math]4\sqrt{\frac{2}{3}}ms^{-1}[/math]

b) the power applied at the start is nothing right due to the initial velocity being 0 seeming it starts from rest so the ending power will be calculated as [math]P=F\cdot v[/math] which I get as [math]96\sqrt{\frac{2}{3}}W[/math]

I feel as though my calculations for velocity is wrong or something is going wrong.

[Anonymous No.9291138]

>>9291119
Banach's fixed point theorem.

[Anonymous No.9291169]

>>9290753
How did they use logarithms? I feel there is something I'm missing here though I'm not particularly sure how to use them in the case of hyperbolic functions. My guess is that it relates to the said functions being represented using exponential (I lack the knowledge to write it out on here using whatever tool you guys use, though its a fraction with multiple exponentials on top essentially). So how do you go from that to logs at once, it just seems like a bit of a step.

[Anonymous No.9291214]

>>9291169
Do you know what arctanh is?

[Anonymous No.9291220]

Do deserts affect global temperature? They're large areas of land where the sun rays hit the ground then just bounce back into space because of nearly no water vapor in the air to trap infrared.

[Anonymous No.9291236]

suppose you are looking at some data over the last 100yrs(eg: height of people). collating everthing you find some distribution. how can you find out whether the distribution changes over time if the sample is on the small side? as the most recent data provide the best indicator but your samples could be victim to variance.

is there some sort of transform for the distribution based on average drift(in mean or something else)?

[Anonymous No.9291239]

>>9291129
idk man, it seems about right
why do you say it's wrong, I get 3.2m/s as well
same goes for the power, I think you did right

[Anonymous No.9291245]

>>9291169
[math] y:=\tanh(x) [/math]
You wanna solve for x which would be arctanh(y)
[math] y= \frac{\sinh(x)}{\cosh(x)} = \frac{e^x-e^{-x}}{e^x+e^{-x}} [/math]
Multiply numerator and demoninator by e^x
[math] y=\frac{ (e^x)^2-1 }{(e^x)^2+1} [/math]
Move the denominator.
[math] (e^x)^2-1 = y ( (e^x)^2+1 ) = y (e^x)^2 + y [/math]
And now you get
[math] (e^x)^2 (1-y) = y+1 [/math]
when y is not 1 (it never is so it's ok) you can write
[math] (e^x)^2 = \frac{y+1}{1-y} [/math]
therefore
[math] e^x = \sqrt{ \frac{y+1}{1-y}} \text{ or } e^x = \sqrt{ \frac{y+1}{1-y}} [/math]
Since e^x is always positive, the second solution is not accepted. You can easily see check that the first solution satisfies the original equation.
From the first solution you get
[math] x = \log \sqrt{ \frac{y+1}{1-y}} = \log (\frac{y+1}{1-y})^{\frac{1}{2}} = \frac{1}{2} \log (\frac{y+1}{1-y}) [/math]

[Anonymous No.9291247]

is it normal that in this correctly bound structure, the global equilibrium equations (which are 3: vertical forces, lateral forces and momentum) have 4 unknown terms (lateral reactions in A and F, vertical reactions in A and E) resulting in the inability of calculating the binding reactions?

[Anonymous No.9291255]

>>9291169
The logarithm is the inverse of the exponential, so if you can represent the hyperbolic trig functions as exponentials, you can represent their inverses using logs.

[Anonymous No.9291263]

Humans came out of the universe, and what we know of as consciousness did as well. Isn't it weird that the universe created a being within itself to explain and discover itself?

[Anonymous No.9291267]

>>9291214
Yep.

>>9291245
>>9291255
At risk of sounding stupid I feel like that was supposed to be way harder, when you put it like that its really strait forward. Thank you tons guys, hope you all have good days ahead.

[Anonymous No.9291269]

>>9291119
let x be a fixed point of this recursion. Then
[math] x = \frac{\alpha +x }{1+x} \Leftrightarrow \alpha = x(1+x) -x = x^2 [/math]
The rest is >>9291138

[Anonymous No.9291399]

Best way to learn MATLAB? I got a summer '18 position recently and said I have experience with it, when really I just use it like a calculator. Specifically for optics in matlab does anyone know good books?

[Anonymous No.9291401]

Can anyone help me understand what a force actually is? I know it results when there's an interaction between two objects, but is this interaction always physical? I can understand force when thinking in terms of idk. an object hitting another object and transfering its energy/momentum. But what exactly IS a force? Is it a term we use to describe the action/period of transfer? As soon as the transfer begins, there's a force, and as soon the force stops, the transfer ceases. What is acceleration describing? Is it describing the period in which the force acts? As soon as the acceleration stops, there's no more force acting on the body. So, is force simply a period of transfer of momenta/energy? Also, this doesn't make much sense when talking about force in terms of charge. How is there a force acting on a charge? What is transferring it physically? How is the force constant if the acceleration of the field isn't constant? Fuck my brain will explode someone just please explain.

[Anonymous No.9291405]

>>9291263
Not really. It's just chemistry.

[Anonymous No.9291407]

>>9291239
What are you getting for the time in part c?

[Anonymous No.9291441]

>>9291407
idk man it's really easy, the acceleration is linear, so you take the space and divide it by average speed
for the second sentence I don't really know what it means

[Anonymous No.9291466]

power = work/time, so time = work/power right? but its not giving me the same answer as the acceleration and velocity is the problem I am having or at least, I dont understand why it isnt.

[Anonymous No.9291700]

So I need to find the thevenin equivalent of this circuit

I know I need to find the voltage drop and the current across those points, but how do I go about that?

[Anonymous No.9291706]

>>9291700
forgot pic

[Anonymous No.9291708]

How to get good at recurrence definitions?

pic related is the sort of stuff I need to be able to do.

[Anonymous No.9291729]

>>9291708
Well. I think it is pretty simple. When doing this you only need to look at the prime example of a recursively defined set, the great natural numbers. The most beautiful set ever conceived. Let's follow their model.

First let's explicitly say that an element is inside the set. I think the simplest element of S would be 1, so let's start with [math] 1 \in S [/math].

Now we need a relation that yields all the other elements from the elements that are already inside. We can do this by including two axioms: Let's say that concatenation is [math] C [/math]. So that for example, [math] C(1,1) = 11 [/math] or [math] C(0110,011) = 0110011 [/math].

With that, let's say:
[math] s \in S \implies C(s,1) \in S [/math]

So because 1 is in S, we know that 11 is in S, and therefore 111 is in S, and on and on and on.

And our second axiom is
[math] s \in S \implies C(00,s) \in S [/math].

So because 1 is in S, so is 001, and 00001 and 000000111111111. etc.

And that's all. I think if Steve Jobs was alive today he'd say: Great jobs.

[Anonymous No.9291746]

>>9291729
>Great jobs.

why do you have to fucking ruin everything

[Anonymous No.9291751]

>>9291746
It's what Steve would say.

[Anonymous No.9291771]

>>9291466
in response to
>>9291441

[Anonymous No.9291802]

>>9291751
Trump is the new Jobs

[Anonymous No.9291874]

>>9291729
I somewhat understand but I just can't grasp how this logically adds up and makes sense. thank you.

[Anonymous No.9291900]

Well, I have this commutator:

[math][A, B] = B[/math]

How is this possible? Which are the values for [math]A[/math] and [math]B[/math]?

[Anonymous No.9291906]

>>9291900
A=B=0 for example

[Anonymous No.9291913]

>>9291399
Anybody?

[Anonymous No.9291914]

>>9291906
There are more possible values? I thought about that case too, but I was wondering at first if there were more values.

[Anonymous No.9291920]

Can somebody help me understand this?

i:=1 to n-1 basically means 1 through the second to last element?

What does j:=1 to n-i mean?

[Anonymous No.9291941]

>>9291914
sure. you got a system of n^2 equations and 2n^2 variables to solve for nxn matrices.
Here's an example
[eqn] A = \begin{bmatrix}
1 & .5\\
.5 & 1
\end{bmatrix},
B=\begin{bmatrix}
.5 & -.5\\
.5 & -.5
\end{bmatrix} [/eqn]

[Anonymous No.9291945]

>>9291920
if your first loop is at i = 2 for example, your second loop is going from 1 to n-2

[Anonymous No.9291973]

>>9291129
>P=F⋅v
Can't do that. As the mass is accelerating during the period, the velocity isn't constant, so you'd have to integrate it:
[eqn]P = \int^{t}_{0} F \cdot dv = \int_0^t F \cdot \frac{dv}{dt}dt = \int_0^t F \cdot a \space dt [/eqn]
But since you don't know the final time, it's easier to just use the dislocation formula
[eqn]S = S_0 + v_0t + \frac{at^2}{2}[/eqn]
[eqn]4m = 0 + 0 + \frac{4t^2}{6}[/eqn]
So, the final time is [math] t = \sqrt{6} [/math], the average velocity during this period is [math]\bar v = \frac{\Delta S}{\Delta t} = \frac{4}{\sqrt{6}} \approx 1,6 \space m/s[/math]. Now you can use the Power formula [math] P = F \cdot v = 24 \cdot \frac{4}{\sqrt{6}} = 39,2 \space W[/math].

To be honest, it is either that or twice that. Hehehe, I got 78,4W by doing the integration for some reason. Hopefully someone will come along and explain to me why the integration is giving me the wrong result.

[Anonymous No.9291982]

>>9291945
So my first loop would be 1-2, and my second loop would be 1-1? If the loop is from 1 to n-1, how can it evaluate the last element?

[Anonymous No.9291987]

>>9291874
Well. Do you understand the natural numbers? They are defined as such:
[math] 1 \in \mathbb{N} \\ n \in \mathbb{N} \implies n+1 \in \mathbb{N} [/math]
(the formal definition uses the succesor function but you know what I mean).

And the idea is that you state that the set contains that element and then you find a rule that connects that element to every other element you want to put inside the set. In the simple case of the natural numbers we start with [math] 1 \in \mathbb{N} [/math]. And the second axiom tells us that [math] 1 \in \mathbb{N} \implies 2 \in \mathbb{N} [/math]. So 2 is in the natural numbers. But if 2 is in the natural numbers so is 3. And then so is 4. And to put it in simple terms, this goes on "forever".

In the case of your set you start with saying that 1 is in S. And then by the two rules I stated

If 1 is in S, so is 11. And so is 001. If 11 is in S so is 111, and 0011. And this goes on forever. Generating all the elements of S.

[Anonymous No.9292002]

>>9291982
>So my first loop would be 1-2, and my second loop would be 1-1
if n=3, yes.

>If the loop is from 1 to n-1, how can it evaluate the last element?
a_n never gets compared to any other elements, but as you can see in the if loop, a_j can get interchanged with a_(j+1), so if j = n-1 and a_j > a_(j-1), a_n changes places with a_(n-1)

[Anonymous No.9292010]

>>9291920
https://en.wikipedia.org/wiki/Bubble_sort
Also there's a typo in your pic. It should be "interchange a_j a_{j-1}".
Consider the boxes in pic related labeled from n to 1, instead of from 1 to n.

[Anonymous No.9292015]

>>9292010
>Consider the boxes in pic related labeled from n to 1, instead of from 1 to n.
nvm

[Anonymous No.9292066]

>>9292002
>so if j = n-1
Isn't i=n-1? How can j be equal to n-1 when it's n-i?

In this case, how will the 1st element interchange with the 2nd element, since it can only be evaluated against a previous element a_(j-1)?

[Anonymous No.9292108]

Am I supposed to know what the hell professors are researching in depth when applying to a PhD from undergrad? All of their research is over my knowledge level but does the first few years get me caught up quick enough? It sounds interesting and the real applications of the research are neat, but I just dont know half the shit they talk about! In photonics and optics btw

[Anonymous No.9292157]

>>9290753
1+1/2+1/3+1/4+1/5+1/6
does this series diverge or converge?

[Anonymous No.9292161]

>>9291401
A force isn't a completely "naturalized" thing. The universe will behave in ways we don't fundamentally understand the causes behind, but we can map the behavior with math, and make models that predict that behavior. "Force" is then just a name we give to different behaviors in the models.

Whether or not there are literal forces as the word intuitively makes it seem, acting on other stuff, is a metaphysical question.

[Anonymous No.9292165]

>>9291401
You can think of force as the rate of change of momentum with time.

[Anonymous No.9292172]

in this problem once I convert to polar, and dV becomes rdzdrd(theta)

Would my theta bounds be from 0 to pi over 4 since it's held within the first octant?

[Anonymous No.9292211]

>>9291401
>Can anyone help me understand what a force actually is?
In F = ma, force is a measurement of the amount of "push" or "pull" needed to change the velocity of a certain mass by a certain amount.

>What is acceleration describing?
An acceleration is a change in velocity. Mass can be thought of as resistance to change in velocity.

>Also, this doesn't make much sense when talking about force in terms of charge.
A charge is a type of force (electromagnetic). There are 3 others: gravity and the 2 nuclear forces, weak and string.
Note that a charge can create a change in velocity (acceleration) in some objects with mass, as descibed in F = ma.

All you're really asking is, "What is a push?" and the answer is that nobody knows, not even Yang or Mills.

[Anonymous No.9292241]

>>9292211
Lol... Weak and strong*

[Anonymous No.9292397]

>>9292010
Actually, if you look closely the picture says
>if a_j > a_(j+1) then interchange a_j and a(j+1)

[Anonymous No.9292468]

>>9292397
holy shit you're right

[Anonymous No.9292491]

Why is Kurisu Makise such a piece of shit whore who deserves to get punched in the face?

[Anonymous No.9292554]

How do #17 lads?

[Anonymous No.9292556]

Why are they called steps outside but stairs inside?

[Anonymous No.9292571]

>>9292172
Yes.

[Anonymous No.9292578]

do you think astronauts have sex in space

[Anonymous No.9292726]

so this is what i've got

AC=x+y
AD=(x+y)+CD
BE=y+CD-x
AE=y+CD
BF=CD-x
DF=-y-x

is there anyway i can express CD with x and y?

[Anonymous No.9293165]

how is min(C)-1-a concluded to be the smallest element of A here? for each c in C, c=a+1+b, where b<a or b=a.

so the min(C) is the smallest case of this, meaning that it has the smallest a and b? and in turn, C-1-a has to be the b that is equal to a that is the smallest element of A?

[Anonymous No.9293280]

Does ionizing radiation actually cause a visual grain-like distortion phenomenon when near an intense enough source, or is this just the theatrical work of video games?

Been playing a few games with nuclear radiation sources, and I just now realized most of them have this effect in one way or another, basically looking like a film grain.

It feels like an obvious answer, however I've been rationalizing it by thinking that any particles that pass through the eye may distort what you see, or your brain would process it like a fuzzy grain image, kind of like how you can sometimes see the white cells passing through your eye's veins.

where can I read up on the various phenomena created by nuclear radiation?

[Anonymous No.9293282]

>>9293165
pretty sure there's a typo and it should be min(C)-1-b

[Anonymous No.9293287]

>>9293280
I'd also add that, contrary to my rationale for its presence in the games, I would assume realistically if particles were entering your body in that area in a sufficient amount to cause that distortion effect, you wouldn't be living anymore after a few hours, let alone seeing.

[Anonymous No.9293311]

>>9291220
Seems like they shouldn't have a positive contribution, but then, my knowledge about climatology is literally from primary school.

Man, those are some sexy dunes.

[Anonymous No.9293312]

>>9291263
Consciousness evolves out of a need for selfpreservation. It's not a mystery.

[Anonymous No.9293347]

>>9293280
You do get bright blue flashes. Other than that no.

[Anonymous No.9293355]

>>9291129
If you're looking for the answer of a.ii), You would use the Kf - Ki = W and 1/2 mv^2 = K

So, (1/2)(18)v^2 = 96 solving for v gives you 1.633 as the final velocity.

I would do c) before b) as you solve for time using d/v and then you can find average power from there then switch over to b) where you integrate and end up with the final power

[Anonymous No.9293361]

>>9291973
There's a few things you could have done differently Δt = Δd/Δv so you could have found out t easily from that after finding v from the W = Kf - Ki equation. (the question said to thing of conservation of energy)

Next, you could have found P through W/t which is *average* power which is 39.2.

This is where you think you are making a mistake because that's only the average. When you integrate it, and apply the final time,(which is what you did) you are finding out the overall power that was given which turns out to be 78.4.

You did everything right, it seems as though you just didn't know exactly what you were looking for.

[Anonymous No.9293436]

>>9293361
I think I get it. But then, average power is a pretty useless physical quantity, as, usually, when you want to know the power of the system, you want to know about all of it, not just most of it. So suppose this particle is a single geared car, the engine would have to be able to give all 80W to keep it accelerating, instead of just 40W? If so, then yeah, average power is pretty useless.

[Anonymous No.9293440]

>>9290753
Why is tan so different from sin and cos (given the the graph is vertical, functions are far different related formulae e.g. addition formulae bears no resemblance)?

[Anonymous No.9293442]

>>9293440
Because instead of tan being directly related to the circle (like sin and cos), we divide sin by cos to get our final tan function.

[Anonymous No.9293450]

Can anyone explain to me in a few words why this is the case in Boolean algebra?
[math](a+\overline{a}b) = (a+b) [/math]

[Anonymous No.9293459]

>>9293450
what is +?

[Anonymous No.9293461]

Help
Is this true, and if so, for any frame?
[math]g^{ad}\Gamma^c_{dc} = 0[/math]

[Anonymous No.9293463]

>>9293459
AND

[Anonymous No.9293466]

>>9293442
That makes more sense, thank-you anon!

[Anonymous No.9293471]

>>9293440
Consider the tangent line at the unit circle at (1,0).
tan(x) is the the (signed) length shown in the graph.

[Anonymous No.9293472]

>>9293440
>>9293471

[Anonymous No.9293475]

If I have a cube with positive charges q lying on the center of each of its faces, what's the electric flux on each of its faces? I'm thinking the total flux of the cube is 6q because of Gauss's law which would mean the flux on each face is q but I'm not so sure.

[Anonymous No.9293480]

>>9292211
>>9292165
>>9292161
Appreciate the responses.

[Anonymous No.9293483]

>>9293463
draw a venn diagram and you'll see it

[Anonymous No.9293484]

>>9293471
>>9293472
I see now, I'll download the images for reference. Thanks a ton guys, it all makes sense.

[Anonymous No.9293572]

What does inductive mean in this context?

[Anonymous No.9293576]

>>9293572
what it says below the blue line ?

[Anonymous No.9293617]

>>9293572
you literally posted the definition

[Anonymous No.9293887]

nigga how the FUCK i do this without a pdf for X

[Anonymous No.9293896]

>>9293887
X is uniformly distributed, so you gotta use that.

[Anonymous No.9293900]

>>9293887
It's badly phrased. Whoever retard wrote this meant X~U(-1,3).

[Anonymous No.9293902]

>>9293887
you don't need it to be explicitly given to you
>>9293896
where is that stated?

let f be the density function of X, then for the density function g of Y you have the property
g(x) = f(x)+f(-x) for 0<x<1
and
g(x) = f(x) 1<x<3

[Anonymous No.9293907]

>>9293902
This: >>9293900
It's not stated because picking a random number without any context always means uniformly distributed, be it discrete or continuous.

[Anonymous No.9293914]

>>9293907

this is what I'm thinking. in the context of how this course has been in the past, I feel the prof would explicitly say 'assume f is the pdf of x' in the question if they wanted an answer as a function of it

[Anonymous No.9293920]

>>9293896
>>9293900

So would you express it as:

p(y) = {1/2 for 0 <= Y <= 1; 1/2 for 1<= Y <= 2; 0 for all other Y}

?

[Anonymous No.9293921]

>>9293907
it's a problem that can be solved without assuming anything about the random variable.
Assuming that the person phrasing the question is an idiot who can't do it properly is kind of presumptuous, don't you think?

[Anonymous No.9293925]

>>9293920

er, 1/2 from 1 <= Y <= 3, not 2, my bad

[Anonymous No.9293929]

>>9293914

he said it's a uniform distribution, so you have the PDF, or can easily compute it since you know the interval. the density gets doubled from [0,1] since that's where abs maps [-1,0] to.

[Anonymous No.9293946]

>>9293929

actually i think that the density at 0 stays the same, but other than that it's pretty straightforward

[Anonymous No.9293956]

>>9293921
Yeah it can be solved without, but then it's just filling in the formula in the theorem, giving you some abstract nonsense pdf.
But this is obviously an "easy" probability question, so yes, without presumptions I can say this that the X is intended to be uniformly distributed. I too sometimes can't believe what an assignment states.

>>9293920
Correct.

[Anonymous No.9293969]

>>9293956

I wouldn't have to worry about 0 not being redundant, since it's just a point on a continuous distribution ergo it doesn't impact the density function, right?

[Anonymous No.9293971]

>>9293920
Yesm that's correct.
I assume you made a typo here: "1<= Y <= 2" cause it should be 1<= Y <= 3

[Anonymous No.9293977]

>>9293971

Ya. Also it should be 1 < Y not 1 < = Y for the second piece

[Anonymous No.9293981]

>Prove that ZFC implies that there are 2^aleph0 countable nonstandard models of Peano arithmetic.

ANY help is appreciated.

[Anonymous No.9293988]

>>9293981
use all initial segments of ordinals up to some big ordinal like 2^aleph0

[Anonymous No.9293998]

>>9293971
>>9293977
Wait now that I thought about again. It's actually incorrect. The PDF doesn't even integrate to 1.
The densities should be 1/2 and 1/4.

[Anonymous No.9294067]

>>9293998

Oh, true. Good catch, I'm dumb.

[Anonymous No.9294080]

How difficult is linear algebra and matrices?
It looks like there's a lot to it.

[Anonymous No.9294086]

>>9294080
easier than most other undergrad mathematics

[Anonymous No.9294088]

>>9294080

Not really difficult if you've never struggled with math. It's just a different thing

Try to get it conceptually, though.

[Anonymous No.9294091]

>>9294080
It is very easy and intuitive when DONE RIGHT.
Make sure to watch this as well:
https://www.youtube.com/playlist?list=PLZHQObOWTQDPD3MizzM2xVFitgF8hE_ab

[Anonymous No.9294481]

Super quick Q:

I'm looking at some basic economic concepts but I drawing a blank on some of the math. What does the function that produces this curve look like?

[Anonymous No.9294485]

>>9294481
depends on the specifics, but for example sqrt or log

[Anonymous No.9294633]

Is Havel–Hakimi necessary or sufficient for vector sequence to be graphic?

[Anonymous No.9294676]

Why do physics books use [math]d\tau[/math] to denote a differential volume element instead of just [math]dV[/math]? I get that [math]V[/math] is used to represent potential, but it should be clear from context whether [math]dV[/math] refers to volume or potential. What about [math]\tau[/math] makes it an intuitive variable for volume?

[Anonymous No.9294765]

The fuck are these random itchy white bumps on my arm? They appear seemingly at random, I can't find any evidence of bugs as I've already washed my bedding material multiple times and these isn't any blood so I don't think they're bite marks

It's just really odd and annoying.

Just a small white bump surrounded by some red skin possibly from light scratching.

[Anonymous No.9294774]

>>9294765
Looks like aids.

[Anonymous No.9294831]

What is the exact resolution and dimensions of the Iphone X with the notch and rounded corners in mind?

[Anonymous No.9294839]

What are some scientifically-proven ways to stop missing my ex-gf?

[Anonymous No.9294869]

>>9294831
Why?

[Anonymous No.9294870]

>>9294765
Could be mosquito bites.

[Anonymous No.9294878]

>>9294870
I don't think so as like 5-6 of them will appear at the same time, and I don't see any blood as if something bit me

[Anonymous No.9294902]

saw this one posted on pol, how do you solve it without using trigonometry, only elementary geometry?

[Anonymous No.9294919]

>>9294902
Wouldn't be enough info

[Anonymous No.9294921]

>>9294919
are you sure?

pic related is an other one and I know how to solve this one wiith only elementary geometry

[Anonymous No.9294926]

Do males get their X-chromosomes from just one of their maternal grandparents, or is it a combination of both from crossing over?

[Anonymous No.9294936]

>>9294902
add up angles and solve linear systems
?=12°

[Anonymous No.9294940]

>>9294921
ur a brainlet, its ok

[Anonymous No.9294944]

>>9294926
>is it a combination of both from crossing over?
Yes

[Anonymous No.9294948]

>>9294902
>>9294919
I think I've tried everything man, never learned trig

[Anonymous No.9294950]

>>9294936
yeah I tried that but which sum of angles includes '?'?

every equation I tried to make the '?'s ended up negating each other because AEC and DEC also include '?'

for example ABECA=360° but because this includes AEC and ECA the '?'s negate each other

[Anonymous No.9294955]

Even if you demonstrate understanding and completion of material (by say, posting your solutions to a series of undergrad books online through github), you can't ever get around having to deal with the drudgery of doing undergrad at a premium price to get into grad school, right? For math btw

[Anonymous No.9295053]

>>9294936
go ahead and post the linear system you used

[Anonymous No.9295059]

what are the big ideas that you learn in organic chemistry?

[Anonymous No.9295066]

>>9290753
What are some interesting applications of the Lenstra Lenstra Lovasz basis reduction algorithm?

[Anonymous No.9295078]

>>9295059
Electrophile moves towards the nucleophile, acid moves towards base. Also....

No that's it actually.

[Anonymous No.9295099]

>>9294940
then go ahead and post how to obtain the solution you fucktard

[Anonymous No.9295139]

>>9294955
some colleges allow you to test out of higher level math classes but not many.

also I've never heard of any grad school accepting "self taught" as an acceptable undergrad college

[Anonymous No.9295210]

>>9294955
After scholarships I think I paid $1500 per semester for university. If you can't put aside $3000 a year through work or loans or mommy and daddy you have serious financial issues. You need to focus on those before whining about why you're not a special enough snowflake to be given acceptance into a math grad school on merit you probably don't have. If you're not resourceful enough to apply to every scholarship you see and get money to fund your undergrad education you don't deserve grad school.

[Anonymous No.9295219]

>>9295078
seriously?

[Anonymous No.9295225]

>>9295219
oh and some stuff with alkenes or something

[Anonymous No.9295235]

>>9295225
thanks

can someone recommend a good organic chem textbooks?

[Anonymous No.9295240]

>>9295235
organic chemistry as a second language is a pretty good textbook

[Anonymous No.9295308]

What is temperature exactly? Why does touching an ice cube make my hand cold when a brick does not do that shit despite both objects being solid? It's also weird to me because cold temperature seems passive.

[Anonymous No.9295347]

>>9295308
Exactly? It's [math]T=\frac {\partial U} {\partial S} [/math] where U is the internal energy and S is entropy. U is defined over U(S,V,N) with V being volume and N being mass.

Ice cubes take the heat off of your hands, and since ice cubes (assuming impure water) are good conductors, your hand loses heat and the ice cube gains energy. The state of mater does have a role in temperature, but it's more important to consider how conductive something is and the relative temperatures.

not sure I did a good job explaining this

[Anonymous No.9295387]

Any Physics fags here?

https://www.icanteachmychild.com/can-you-blow-up-a-balloon-in-a-bottle/

What's the specific law that's behind the science of this experiment? Basically, you put a balloon inside a bottle (with the open end of the balloon stretched and attached unto the bottle opening). then you blow into the bottle, but you can't
'cause there's still air inside.

[Anonymous No.9295417]

>>9295387
By blowing air into the bottle you increase the pressure or air density in the bottle. This means you need to exhale air at a higher rate per meter cubed the more air there is in the balloon.

If you used a compressor, to blow for you, the balloon would pop well before the bottle gets full since the force needed to combat the pressure would be too much for the balloon to handle.

[Anonymous No.9295467]

>>9295417
>>9295387
Someone from /b/ told me that it can be related to boyle's law. Mind explaining it for me?

[Anonymous No.9295487]

>>9295467
It can in a way but it's somewhat difficult to describe it like this.

Basically, Boyle's law states that PV=k, or as you've probably seen it in your chemistry class, P1V1=P2V2. Either way, P=k/V where k is just some constant.
As pressure increases in the bottle, the volume decreases because the pressure is going into the balloon. When we say PV=k, we expect that if one increases, the other decreases (since k is constant)

The force you feel when you try to blow air into it is the pressure in the bottle. As you inflate the balloon you decrease the volume of the bottle (volume of the bottle = volume of empty bottle - volume of balloon). This increases the pressure since P1V1=P2V2, and V1>V2.

[Anonymous No.9295518]

>>9295487
Wait, so I'm a confused brainlet

The guy from /b/ said, "however, when its inside the bottle, theres nowhere for the air to be displaced, this causes an increase in pressure of the system, but no change in volume." (this is assuming there's no hole on the bottle)

and thatseems to coincide with what you're saying but then the /b/ guy says something along the lines of "When you blow into a balloon you attempt to increase the volume inside of it. This displaces the air around it." (a balloon thats not in a bottle)

but didn't you say in one of your posts that by blowing air into the bottle you increase the pressure or air density in the bottle?

[Anonymous No.9295585]

I've done a year of college taking a pretty wide variety of classes, mostly sciences.

Every single subject except math has relied on answering very broad questions and getting told I'm wrong for not giving the answer that the lecturer/tutor/random fuckwit thought of. As in, you could come up with a suitable answer based on the information you have but still be wrong. Whether or not your right boils down to magically coming to the same conclusions as whoever wrote the question.

It has pissed me off to not end and might even fail me. Will all of my college level science subjects be like this?

[Anonymous No.9295642]

anyone here use discord, I'm getting ready to take an online math test for a job and would like to send someone the questions rapid fire style. it probably wouldn't take longer than 4 minutes. I'd be your best friend?! also I'm a trans girl and will send you nudes.

[Anonymous No.9295649]

>>9295642
https://discord.gg/MmDKfP anyone is free to join. I named it mathscience so if you're inclined feel free to use it

[Anonymous No.9295670]

>>9294948
Hey wait, can I subtract the 231 from the 309?

Because that gets me to 12, well on the wrong triangle anyways....

[Anonymous No.9295682]

>>9290753
about 3ft

[Anonymous No.9295686]

>>9290753

how can light have momentum but no mass?

[Anonymous No.9295697]

>>9295670
>>9294902
>>9294919
Hey well I don't understand the math I just did

but fucking around with some pie charts for the subtraction I got 78 for the total on the 51

overlaying the pie charts seems to confirm this

Are you proud of me /sci/? Or am I wrong?

[Anonymous No.9295698]

>>9295686
Light is composed of photons, so we could ask if the photon has mass. The answer is then definitely "no": the photon is a massless particle. According to theory it has energy and momentum but no mass, and this is confirmed by experiment to within strict limits.

[Anonymous No.9295711]

retard here
can someone please explain why this is true

[Anonymous No.9295784]

>>9295698
you didn't fucking answer his question you moron

[Anonymous No.9295793]

If the torque at shaft 2 is 10Nm and the gear ratio is 1:2 does that mean the motor driving shaft 1 has and output of 5Nm?

[Anonymous No.9295845]

>>9294878
Every mosquito bite I've ever had has looked exactly like that. Mosquitos aren't messy eaters.

[Anonymous No.9295902]

>>9295308
Diffusion of microscopic movement. Jiggly energy in your hand leaks onto the icecube. The difference between something feeling cold or not is based on temperature differential and conductivity. For example metals easily feel very hot or very cold because they conduct heat rapidly. Ice is just usually much colder than your skin.

[Anonymous No.9295914]

>>9295686
Mass is not a fundamental property of energy. You can have a bunch of photons in a volume and they'll weigh nothing. Put a box around them and they exert force on the box, and even if the box is weightless this pressure will confer weight to the box-photon system.

[Anonymous No.9295937]

Is this book good for a first course in LinAlg?
I mean with matrices and shit
I will do Axler later

[Anonymous No.9295949]

How much signals do I need to know before taking a book on Control Theory?

[Anonymous No.9296011]

I never once had questions like this back in high school, I don't know why my college has such a hard on for them but MAN are they annoying

it's like the "Train A departs the station at..." questions of this generation

[Anonymous No.9296022]

I'm considering taking Precalc and Trig in the same semester so I get all the math prereqs out of the way for computer science in my upper division classes

from what I can tell, trigonometry is stupid simple even for someone who's bad at math (which is why I'm taking these courses now rather than having taken them in High School)
am I woefully misinformed and this is a terrible idea, or could it be possible?

[Anonymous No.9296038]

>>9296011
Is it 9 gallons?

[Anonymous No.9296041]

>>9296038
yes

[Anonymous No.9296061]

>>9295937
>LinAlg
>good
Only if you are an engineer.

[Anonymous No.9296070]

>>9295518
Sorry I went to bed.

Consider the closed system of your puffed up cheeks full of air against the bottle itself without a balloon. As you blow (i.e. using your muscles to close your cheeks) you decrease the total volume in the system but increase the pressure. This follows Boyle's law.

Also I should note that when you said
>(this is assuming there's no hole on the bottle)
You are actually incorrect. By poking a hole in the bottle you've just expanded the system to the entire universe. You might ask, then, why the entire universe isn't at the exact same pressure, the answer to this is the fact that the universe isn't an ideal gas.

And in case I wasn't clear, when the balloon is in the bottle and you blow air into it, you're decreasing the volume in the bottle but increasing the pressure, which is in accordance with Boyle's law.

[Anonymous No.9296078]

>>9295914
How can something massless provide a force? Are we using the definition of F=dp/dt?

[Anonymous No.9296079]

Does analysis get ""easier"" the more you go into it? My analysis course doesn't even talk of metric space or topology and a lot of things would seem more intuitive having addressed these seemingly "advanced" topics.

[Anonymous No.9296086]

>>9296079
>the more you go into it
Analysis is fucking garbage so you shouldn't "go into it" at all.
>My analysis course doesn't even talk of metric space or topology
It's shit then.

[Anonymous No.9296091]

>>9296086
fuck off

>>9296079
Your prof. should have introduced metric spaces properly before going into them. Did he not? The basic properties (a good definition and a couple examples) should be enough.

It will get easier the more you start understanding the topology of a metric space.

[Anonymous No.9296095]

Can i use the triple equal sign to indicate logical equivalence when talking about two implicit differentiation relations?

[Anonymous No.9296098]

>>9296079
>>9296091
on the other hand, if your prof. is deliberately avoiding the mention of topology or metric space in order to focus on the specific properties of R or R^n, that's a reasonable approach to take. understand the properties of R^n first before you try to abstract.

[Anonymous No.9296141]

>>9296095
just use [math]\implies[/math]

[Anonymous No.9296176]

>>9295793
>>9295793
if shaft 2's gear has twice as many "teeth" or pinions or whatever you call em, yes of course. providing nothing's lost in translation. it'll also turn at half the speed. which is why a small engine can move a car given the appropriate gearbox.


>let's get to the point

I guess many brainlets like me ask this every other minute, but can you really/ is it worth studying maths and physics when you're, say, 30?
>obv given that you have the money and time to do so

I've been toying with the idea for a few years but I didn't care about math when I was a kid so idk if the brain damage will be reversible. needless to say if I get to it I'd give it my 125%. I majored in Classical Scholarship at college and I did fairly well, but I also know (because I complained the most back then) that college nowadays is a joke.

I know I'd be able to handle a scientific-themed highschool degree (in my country, the last 2 yrs of highchool you can decide most of your subjects - I'd go for hard math, phys, chems and whatever else they offer). But I'm not sure whether higher education (college, uni) would be within my reach or not.

[Anonymous No.9296183]

>>9296176
forgot to post pic

[Anonymous No.9296239]

>tfw it only took my three hours to understand related rates
Am I the smartest man alive?

[Anonymous No.9296266]

>>9295845
It looks like I'm allergic to mosquito bites, not if only I could find and kill the fucker, my room is pretty much sealed off so I don't know how it got in.

[Anonymous No.9296353]

Did I translate this right?
"For every x in set S, there exists only one x for every y such that f(x)=y. Therefor, S is a function"
[eqn]∀\it{x}∈S,∃!\it{x}:f(x)=y[/eqn]∴S is a function

[Anonymous No.9296354]

>>9296078
For things that have no mass:

E = (hc/ λ)

[Anonymous No.9296356]

Did I translate this right?
"For every x in set S, there exists only one x for every y such that f(x)=y. Therefor, S is a function"
[math]∀\it{x}∈S,∃!\it{x}:f(x)=y[/math]∴S is a function

[Anonymous No.9296361]

>>9296356
fuck it, I tried.
∀x∈S,∃!x:f(x)=y∴S is a function

[Anonymous No.9296452]

>>9296353
>>9296356
>>9296361
yes
now please stop with the autism
also the tex for it is \therefore

[Anonymous No.9296475]

The system
[math]\dot{x}=y(1+x-y^2)\\ \dot{y}=x(1+y-x^2)[/math]
has 6 equilibrium points, right?

[Anonymous No.9296478]

>>9295210
I'm getting by just fine, m8. I get fasfa and have worked myself into having an ok savings and income for what that doesn't cover. It'd just be nice if proving merit alone was an option.

I always intend to apply for scholarships too, but feel I'd be drowned out in the sea applicants since I'm just an average white CIS male with a non-stellar GPA. But props to you for getting them, I think I'll actually apply around this year.

[Anonymous No.9296488]

>>9296478
I just go to a shit school, and will at best probably only ever get into a mid-tier school, and that feeling kinda sucks and makes me wish merit was weighed more heavily.

[Anonymous No.9296493]

What did they do here to go from one form to the other? I've tried the conjugate and everything.

[Anonymous No.9296504]

>>9296475
7
http://www.wolframalpha.com/input/?i=y(1%2Bx-y%5E2)+%3D+x(1%2By-x%5E2)++%3D+0

[Anonymous No.9296505]

>>9296493
They just made the fractions have the same denominator in order to add them.

[Anonymous No.9296511]

>>9296493
[math] \frac{a}{b} - \frac{c}{d} = \frac{ad-cb}{bd} [/math]

[Anonymous No.9296518]

>>9296493
they're just multiplying to get a common denominator

[math] \frac{1}{x+ \Delta x} \cdot \frac{x}{x} - \frac{1}{x} \cdot \frac{x + \Delta x}{x + \Delta x} [/math]

[Anonymous No.9296527]

>>9296511
>>9296518

Thanks guys, its always these stupid easy rules I forgot that catch me out.

[Anonymous No.9296539]

>>9296504
fuck i forgot the 1/2-\sqrt(5)/2 one.
thanks

[Anonymous No.9296561]

how do I socialize ?

[Anonymous No.9296596]

>For what values of x is the matrix A below invertible?
>[-2x 3]
>[6 6]

What's it asking for here? To find out what x should be greater/smaller than for the matrix to be invertible?

3*6 = 18 so -2x * 6 would need to = -18 for the matrix not to be invertible.
If x were 1.5 then it wouldn't be invertible. So is the answer just !=1.5?

[Anonymous No.9296603]

>>9296596
you fucked up, it's -1.5
otherwise you're right

[Anonymous No.9296607]

>>9296603
Thanks.
I wish the question wasn't worded in this way.

[Anonymous No.9296673]

what are some books/resources on linear algebra? i'm not a math major and a lot of the stuff in other books just seems to go over my head. i feel like i'm way out of my depth here.

[Anonymous No.9296695]

>>9296561
always join the group activities

[Anonymous No.9296707]

Am I a brainlet? The solution should be undefined at t=0 right? I'm getting (t^3-t^2+1)/(3t)

[Anonymous No.9296726]

>>9294921
The scale on that one is completely wrong, the 10 on the top right looks like thie 20 on the bottom left

[Anonymous No.9296727]

>>9296707
that's a division symbol, not a plus

[Anonymous No.9296741]

>>9296727
fug

[Anonymous No.9296748]

>>9296078
I don't know if that applies. I'm just paraphrasing a lecture by Susskind.

[Anonymous No.9296897]

How do I use the fact that (for Legendre polynomials) [math]\sum\limits_{m=0}^\infty P_m(\cos\theta) =\frac{1}{2 \sin{\frac{\theta}{2}}}[/math] to calculate the integral [math]\int_0^\pi \frac{\sin\theta\cos^2\theta}{\sin{\frac{\theta}{2}}} d\theta[/math]? I know it becomes [math]\int_0^\pi 2\sin\theta\cos^2\theta \sum\limits_{m=0}^\infty P_m(\cos\theta) d\theta[/math], but I don't see how I'm supposed to use this here.

[Simon No.9296906]

>>9294921
I

[Anonymous No.9296911]

>>9296897
try substituting arccos

[Anonymous No.9296951]

aerospace engineer with a 2.75 GPA. Should I even apply to jobs online, where almost all say 3.0 nd above are required?

[Anonymous No.9296957]

>>9296673
You could try Savov's "No Bullshit" books or Lay's (not Lax's) book.

[Anonymous No.9296961]

>>9296561
Act the way you'd like other people to act, and relax and be patient.

[Anonymous No.9296982]

>>9296897
>>9296911
substitution with [math] \cos^{-1} [/math]. together with [math] \sin(\cos^{-1}(x)) = \sqrt{1-x^2} [/math] and [math] \frac{\mathrm{d} }{\mathrm{d} x}\cos^{-1}(x) =-\frac{1}{ \sqrt{1-x^2}} [/math] gives us
[eqn] \int_0^\pi 2\sin\theta\cos^2\theta \sum\limits_{m=0}^\infty P_m(\cos\theta) d\theta = 2 \int_{-1}^1 x^2 \sum\limits_{m=0}^\infty P_m(x) dx [/eqn]
Now we use
[eqn] x^2 = \frac{2}{3} \left( \frac{3}{2} x^2 - \frac{1}{2} +\frac{1}{2} \right) =\frac{2}{3} \left(P_2(x) + \frac{1}{2} P_0(x) \right) [/eqn]
and the orthogonality of the legendre polynomials to reduce the integral to
[eqn] 2 \int_{-1}^1 \frac{2}{3}P_2(x)^2+\frac{1}{3}P_0(x)^2dx = \frac{4}{3} \frac{2}{5} +\frac{2}{3} 2 = \frac{28}{15}[/eqn]

[Anonymous No.9297009]

I saw what looked like a bug on the wall but upon closer examination it was lint.
When I returned a few hours later in the same spot was a house centipede.
Can life form from inanimate matter?

[Simon No.9297021]

Who Let The UnderAge People On My Board?

1000000 e^2 + 1

7.38905709893065022723042746057500781318031557055184732... × 10^6

1000000 E^2 + 16^^1

1.1654330404563..._7×7^8

[Anonymous No.9297236]

Can someone help me with:
>>>/wsr/413880
Thanks.

[Anonymous No.9297263]

>>9296726
the scale is wrong to prevent dummies from cheating

and its actually a very interesting problem that has a creative solution

[Anonymous No.9297304]

>>9297236
okay its the middle of the night here and I suck in physics but let me try... gimme a moment

[Anonymous No.9297319]

>>9297236
>>9297304
3. a
assume the speed is 0 at point A that means kinetic energy at points B and C are equivalent to the potential energy transformed

formula for potential energy simplified is [math]mgh[/math], kinetic energy is [math]\frac{mv^{2}}{2}[/math]

now solve for v which is.. uhmm [math]v=\sqrt{2gh}[/math]

h is the height difference so for B it is 1.8m and for C it is 3m. plug it into the equation for each point and you have the speed. because there is no friction the speed is path independent and only depends on the difference of altitude

3. b
[math]W=mgh[/math]

h is 3m, m is 50kg, choose g as you wish and you are done. once again the work is path independent and would even be friction independent

4. I have no idea what "is the work conservative" means. anyway once again path independent so just plug the displacement of the start and the end point relative to the force vector and you have the answer. so basically F*d in vector form of dimensions 2

axes arent even named and it is really hard for me to understand what is even going on but I think the force goes to top right with 2N along each axis. since the displacement is (2,0) and the force is (2,2) the answer is 4

6. elastic energy of a spring is basically the same as kinetic energy because the restoring force is F=k*x

so elastic energy is [math]\frac{kx^{2}}{2}[/math]

now once again convert potential into kinetic energy just this time its actually elastic energy so the equation will be a bit different because m doesnt cancel out

[math]d=\sqrt{\frac{2mgh}{K}}[/math]

plug it in, K=1000, m=1.5kg, h=1m, g as you please, hmm and that should be all of it

[Anonymous No.9297320]

>>9297304
thanks, bro.

[Anonymous No.9297326]

>>9297304
>>9297319
Thank you very much, man. I really appreciate it.

[Anonymous No.9297329]

>>9297326
well try to understand the underlying concepts

conservation of energy, path independence. you really need to understand these

[Anonymous No.9297352]

>>9297263
Fuck it, ain't trying to deal with some not to scale BS diagram with 4 missing angles left.

[Anonymous No.9297357]

>>9297352
well there is only 1 unknown

if you have 1 of the remaining angles you know all of them

protip: you can solve it via equivalent angles

[Anonymous No.9297361]

>>9297357
Still too much work, I don't even understand how I solved the other one as I just guessed

[Anonymous No.9297366]

>>9297361
you didnt solve the other one

your solution makes no sense and is just random coincidence because an other anon revealed that the solution is 12° and you just looked for a way to get to 12° of which there are several others, all equally wrong

[Anonymous No.9297369]

>>9295670
>>9295697
Why would you subtract those two? Neither of them include any of the lines you want. it's like trying to find the weight of an orange by subtracting an apple from a grapefruit.

[Anonymous No.9297370]

>>9297366
No I didn't? I solved for the 309 and 231 subtracted those which ended up giving me 78 for that section, subtract 51 from 78 to find the last piece of the puzzle and the rest worked out to 12.

I then confirmed the result by overlaying some pie charts.

[Anonymous No.9297372]

>>9295670
In what world does 309 - 231 = 12

[Anonymous No.9297373]

Literally have no idea how to compute cycle products. What would be the product of (1 2 3)(2 3 4)(5 6 7)(7 8 9 10) as disjoint cycles?

[Anonymous No.9297386]

>>9297372
>>9297369
Was it just a giant coincidence that subtracting those numbers gave me 78? As 78 looks to be correct as I check it by measuring the other polygons you can make with it. Namely ABCE = 360

[Anonymous No.9297392]

>>9297370
>>9297386
The only way you have a solution is if it's repeatable with different numbers.

So lets say the angle CAE is 33 instead of 15 and the whole thing is symmetrical. It wouldn't change the 309 or the 231 so the 78 would be the same and you would get a problem because 78 isn't twice 51.

78 is just 129-51 which is nothing.

it was a coincidence

[Anonymous No.9297393]

>>9297373
(1 3) (2 4) (5 6 8 9 10 7)
(1 2 3)(2 3 4) doesn't overlap with (5 6 7)(7 8 9 10)
(1 2 3)(2 3 4) = (1 3) (2 4)
pick 1, 1 goes to 2, then 2 goes to 3, thus we have (1 3...)
pick 3, 3 goes to 1, then 1 doesn't change so we actually have (1 3)
pick 2, 2 goes to 3, then 3 goes to 4, thus we have (2 4..)
pick 4, 4 doesn't change, then 4 goes to 2 so we have (2 4)
thus (1 3)(2 4)
(5 6 7)(7 8 9 10) = (5 6 8 9 10 7)


Not sure if I helped.

[Anonymous No.9297399]

>>9297366
I don't think this has "1" solution, I got a 4x4 matrix and it has rank 3

[Anonymous No.9297404]

>>9297393
I think it should be done from right to left since it's basically function composition

[Anonymous No.9297405]

>>9297399
it has 1 solution, which you can obtain via trigonometric functions, meaning tangens sine and cosine to actually calculate the geometry

though I do not see how it is solveable without them. I think I have been trolled by one of those nerd baits, an impossible problem that retarded nerds will try to solve

>pic somewhat related
some random shit I tried

[Anonymous No.9297409]

>>9297405
I didn't need trig to solve it. Yall just weak.

[Anonymous No.9297411]

>>9297409
you didnt solve it

[Anonymous No.9297413]

>>9297411
I totally solved it by measuring some other angles from other polygons then subtracting them. The math shows it. I just don't know why it worked.

[Anonymous No.9297419]

>>9297404
It's usually a matter of preference. I wanna say most do it from left to right, just because it's less ackward.

[Anonymous No.9297425]

>>9297413
what you did was assume that BEC=AEB-DEB=129°-51°=78°

subtract 51° and you get 27°, subtract 15° and you get 12°

thats just a coincidence, just like 51°-39°=12° or 39°-15°=2*12° or 36°=3*12° or 30°-18°=12°

there are countless ways to somewhere calculate 12° and they are all coincidental but you are too arrogant and unintelligent to realize

[Anonymous No.9297435]

>>9297425

[Anonymous No.9297442]

>>9297435
changing the 15° angle on point A into 14° and the coincidence is eliminated and you are fucked

[Anonymous No.9297458]

why is there no gate current but we can still find a drain current doing KVL at the input loop of a mosfet in DC analysis

[Anonymous No.9297459]

>>9293572
does a set of all sets include itself

[Anonymous No.9297460]

>>9297442
It changed it to a 13, checking stuff makes it seem like that checks out.

[Anonymous No.9297469]

>>9297460
OK hotshot change it to 33 like I said here >>9297392

[Anonymous No.9297475]

>>9297460
wrong

the actual angle is ~11.37°

and indeed obviously the angle becomes smaller not larger like you assumed because your method is bullshit and it was just a coincidence and yet somehow you are still too arrogant and retarded to admit it

[Anonymous No.9297478]

>>9297475
It still worked. Don't need your fancy correct math in here.

[Anonymous No.9297480]

>>9297478
>Don't need your fancy correct math in here.
2+2 = whatever the fuck I want fuck you

[Anonymous No.9297483]

>>9297478
>>9297475
>>9297469
Plugging in 33 did not work with my newly discovered formula subtracting some random angles, I may need to adjust it.

[Anonymous No.9297486]

Please help /sci/ I'm retarded.

I'm trying to negate a statement and I'm not sure if I'm right. Specifically the definition of a surjective function.

>Assume f:A->B is a function and is not surjective. That is, for all b in B, there does not exist an a in A with f(a)=b

The original definition I'm using is
>a function is surjective if for every b in B there is an a in A with f(a)=b

Please note. The first part of my proof "assume f is a function" is necessary. I just need the negation of surjection for a contrapositive proof

[Anonymous No.9297487]

>>9297478
>>9297483
the absolute state of /sci/

[Anonymous No.9297489]

>>9297483
Yeah it's a shame, the "subtract random shit" theorem could have gotten you a Nobel prize if it worked every time.

[Anonymous No.9297495]

>>9297489
which one? medicine?

[Anonymous No.9297499]

>>9297495
I mean, It's surely applicable to all fields.

[Anonymous No.9297544]

>>9297486
>That is, for all b in B, there does not exist an a in A with f(a)=b
Don't you see how retarded this is? No element from A is sent to B.

Negation of [math] \forall [/math] is [math] \exists [/math] .
Negation of [math] \exists [/math] is [math] \forall [/math] .

[Anonymous No.9297585]

>>9294936
>>9295053
yes please. I can't tell if I'm retarded or if there's no such system for this one.

Wasn't this just a guessing game? Isn't that a legit way of solving this?

[Anonymous No.9297606]

In String Theory, if a string is the fundamental particle, what happens if I chop one in half?

[Anonymous No.9297609]

>>9296911
>>9296982
Thanks! You really helped me a lot! <3

[Anonymous No.9297629]

>>9297544
Thanks. On another note how do you get to [math]\not\exists[/math] with a negation? I have this bad habit of negating existence to that.

[Anonymous No.9297688]

>>9297629
>On another note how do you get to ∄ with a negation?.
[math] \nexists x : P(x) [/math] means [math] \forall x : \neg P(x) [/math] .
It is shorthand for [math] \neg ( \exists x : P(x) ) [/math] and you shouldn't use it desu. It's a pretty bad notation. I never see in textbooks.

[Anonymous No.9297738]

I'm confused about the directions. What I tried so far is simply filling out a Karnaugh map and then creating a boolean function out of all the cells with a 0 in the form of sum of minterms.

But I can't figure out if this is correct and if there is anything different with the function in b.).

Pulling an all nighter and desperate to finish this.

[Anonymous No.9297843]

>>9297475
how'd you come up with that?

[Anonymous No.9297905]

Hey guys, I'm required to do a short undergrad chemistry research project(3 months) on some topic. (Organic or Inorganic)
Could some kind anon point out some topics and/or sources for me to start off with?
(I have no clue how to go about any of this and my professor will only help me if I have an idea)
Thanks in advance

[Anonymous No.9297916]

>>9297009
yes, somehow, but this was not what happened on that spot on your wall

[Anonymous No.9297936]

How do you turn a verbose description of a grammar into EBNF? Is there a trick?

[Anonymous No.9298006]

>>9297843
I plotted it real quick and measured the angle

well I could have calculated it with a calculator but because I had already plotted the basic triangle I only had to change the angle so that was a lot faster

[Anonymous No.9298015]

>>9298006
I forgot to mention: the angle is measured automatically by the program I used so measuring means the program calculated it automatically for me

[Anonymous No.9298024]

Need help with my basic ODE homework please.

'''There has been a test explosion of a nuclear device underwater and the temperature has since risen. The original temperature is assumed to be 20C constantly.

Let T be the temperature at the bottom of the sea. Measurements show that after the explosion, which we assume take place at t=0, the change of temperature at the bottom of the ocean is proportional with the difference between the surface and bottom temperature.''''

a) write an DE with variable T which satisfies the above scenario, and solve when when time t=0 is 25C

b) How long until the temperature is 21*c when measurements who that the temperature is 22c after t = 3 (we can assume as before that the temperature is 25C t = 0)

the DE i ended up with is

dy/dt = T-20 >solved to> T = +/- sqrt(40t)+ 25(when t=0 as stated in question)

but i don't understand how to solve b) so i'm having doubt that my solution for a is right and i'm worried i'm misunderstanding.

sorry for poor english

[Anonymous No.9298029]

>>9291220
deserts aren't randomly sprinkled all over

[Anonymous No.9298042]

>>9298024
you dont know your proportionality constant yet. your ode should be
dy/dt = a*(T-20)
if "original temperature" can be understood as surface temperature
The question is worded pretty badly or you're just bad at translating

[Anonymous No.9298056]

>>9298042
yes original temperature can be understood as surface temperature

thanks

[Anonymous No.9298077]

>>9290753
How much studying is required to make Ted Kaczynski look like a joke?

[Anonymous No.9298086]

>>9291220
yeah like you said, long wave escapes to space easily that's why deserts get cold at night

[Anonymous No.9298088]

>>9297606
Your pants fall down.

[Anonymous No.9298462]

Testing [math]sec(\theta)=\sqrt{1+\frac{4}{c^2}u^2}[/math]
Then, obviously, [math]\Psi[x][/math], however,
[math]\alpha[/math] and so

[Anonymous No.9298471]

Isn't it just half the time? How would I go about proving it using vector calc?

[Anonymous No.9298473]

>>9298471
This would be the parabola

[Anonymous No.9298487]

>>9294765
allergies

[Anonymous No.9298490]

Can someone state the elements of the following set for me? {y2 | (y ∈ N) ∧ (y < 5)}, it should just be y(squared) is an element of the set A where y is a natural number and y is less than 5, right?

[Anonymous No.9298494]

>>9298471
You have to assume that the particle moves with a constant speed.

The given information gives you the speed namely
[eqn] v = \frac{\int_0^c \sqrt{1 + \left(1 - \frac{2x}{c} \right)^2} dx}{T}[/eqn]

Now the time it takes is just the distance divided by the speed
[eqn] \frac{\int_{\frac{c}{2}}^c \sqrt{1 + \left(1 - \frac{2x}{c} \right)^2} dx}{\frac{\int_0^c \sqrt{1 + \left(1 - \frac{2x}{c} \right)^2} dx}{T}} [/eqn]

[Anonymous No.9298497]

>>9298490
yes, so 1,4,9,16

[Anonymous No.9298501]

>>9298497
Okay, I thought so. Thanks!

What about P(P(P(O))), would that be A = {O, 1}?

[Anonymous No.9298504]

>>9298501
>>9298497
O being the empty set in this case, my bad.

[Anonymous No.9298510]

>>9298501
No, clearly P(P(P(O))) has 2^(2^(2^0)) elements.

[Anonymous No.9298528]

>>9298497
>[math] 0 \notin \mathbb{N} [/math]
>>9298501
[math] P(\emptyset) = \{\emptyset\},P(P(\emptyset)) = \{\emptyset, \{\emptyset \}\},P(P(P(\emptyset))) = \{\emptyset, \{\emptyset \},\{\{\emptyset \}\},\{\emptyset, \{\emptyset \}\}\} [/math]

[Anonymous No.9298532]

>>9298504
[math]\{\emptyset,\{\emptyset\},\{\{\emptyset\}\},\{\emptyset,\{\emptyset\}\}\}[\math]

Don't do [math]\{\emptyset\}=1[/math]

[Anonymous No.9298540]

>>9298532
fucking hell
answer is [math]\{\emptyset,\{\emptyset\},\{\{\emptyset\}\},\{\emptyset,\{\emptyset\}\}\}[/math]

dont do [math]\{\emptyset\}=1[/math]

[Anonymous No.9298566]

>>9296011
(6+y)*0.8 = 6*0.5+ y
solve for y

[Anonymous No.9298576]

>>9298528
>>9298532
>>9298540
Thanks a lot, I can absolutely see how you came to the answer when it's formatted in that way.

(Should I include 0 in the set {1, 4, 9, 16}? It's not explicitly defined as a natural number, but as a non-negative, no?)

[Anonymous No.9298584]

>>9298576
depends on how you define the natural numbers.
some heretics define it without containing 0

[Anonymous No.9298609]

How can I get Matlab to interpret my 1x500x500 array as a 500x500? It's having problems with it being 1x500x500 even though it's basically the same as a 500x500

[Anonymous No.9298612]

If I dissolved 300 grams of salt in 10 litres of water, what would be the density of the solution? Assuming no specific temperature and assuming the volume remains constant.

Is the correct answer 1030kg/m^3?

[Anonymous No.9298618]

>>9298609
if x is your array, reshape(x,500,500) should work

[Anonymous No.9298619]

What's the "proper" way to solve something like:
[math]x+2 = 2x-3[/math]
I chanced upon x=5 which is right but obviously if it were more complex that wouldn't be viable.
How are you "meant" to solve it?

[Anonymous No.9298626]

>>9298618
Brilliant thanks, I was trying things like A(1, :, :) = [] but that didn't work for obvious reasons

[Anonymous No.9298633]

>>9298612

D = m/v

Mass of sol'n = mass of water + mass salt added
= 10,000 g + 300g = 10,300 g.

D = 10,300 g / 10,000 mL

= 1.03 g/cm^3.

[Anonymous No.9298635]

How would you go about proving a statement like "A ∪ (B ∪ C) = (A ∪ B) ∪ C"?

[Anonymous No.9298638]

>>9298635
I'm assuming perhaps you could define a universe and then some elements in each set and then proving that each statement is a proper-subsets of the other?

[Anonymous No.9298639]

>>9290753
Is [math]\mathbb{R}^n[/math] a spae of all n-length tuples or column vectors?

[Anonymous No.9298640]

>>9298633
So my answer is correct, you've just done in grams instead of kg. Thanks.

[Anonymous No.9298644]

>>9298639
whatever you want it to be. In the end it's just one of many representations.

[Anonymous No.9298661]

>>9298635
[math]\forall a \in A \cup (B \cup C) [/math]
[math]\iff a\in A \lor a \in B \cup C [/math]
[math]\iff a\in A \lor (a \in B \lor a \in C) [/math]
(check with truth tables)
[math]\iff (a\in A \lor a \in B) \lor a \in C [/math]
[math]\iff a\in A \cup B \lor a \in C [/math]
[math]\iff a\in (A \cup B) \cup C [/math]


[math](a \in (A \cup B) \cup C \iff a \in A \cup (B \cup C)) [/math]
[math]\iff (A \cup B) \cup C = A \cup (B \cup C) [/math]

[Anonymous No.9298666]

Need some help. I tried emailing my professor about it, but she hasn't replied back and it's due tomorrow.

We're doing Arithmetic series'. Prof. gave an example in class, but I don't really understand it, and I think she forgot to post the lecture notes so all I have are my Egyptian hieroglyphics-esc notes.

Basically, the example was "What is the sum of the sequence '10,5,0,-5,.....,-5m' The answer she gave and I wrote down was (10-5m)(m+3)/2. But I think I missed some steps in between somewhere.

I know the pattern for it is f(n) = f(n-1) -5
f(1) = 10
But I really don't understand how it ends up in the form it does.

This is not a question I need to do in my homework, it's the example problem she gave during class. If I could understand how to do this example, I know I could do the ones like it in my homework.

[Anonymous No.9298676]

>>9298666
the pattern is [math] f(n) = 10-5n [/math]
the sum is
[eqn] \sum_{n=0}^{m+2} f(n) = \sum_{n=0}^{m+2} (10-5n) = 10 \left ( \sum_{n=0}^{m+2}1 \right ) - 5 \left ( \sum_{n=0}^{m+2}n \right ) = 10(m+3) -5\frac{(m+2)(m+3)}{2} = \frac{(m+3)(10-5m)}{2}
[/eqn]

[Anonymous No.9298687]

>>9298676
Where does the m+2 come from in that?

[Anonymous No.9298688]

It's been about a trillion years since I've done basic geometry shit.

For a given point on X/Y coordinate, I need to calculate the end-point of a line of given length L with a degree rotation of D.
So if I'm at (-1, 2) and have a rotation of 270deg, and a line length of 0.5, how do?
I'm trying to calculate a "look-ahead" value for reading data out of a texture map from given points and direction but I can't seem to get the math right.

[Anonymous No.9298690]

>>9298687
[math] f(m+2) = -5m [/math]

[Anonymous No.9298695]

>>9298688
[math] (-1,2) + L \cdot (\cos(270°),sin(270°) [/math]

[Anonymous No.9298704]

>>9298695
Cool. That's what I've been doing, I guess I'm fucking something up in world-space coordinates.

[Anonymous No.9298768]

How would I go about proving A ∩ (/) = (/)?

[Anonymous No.9298786]

>>9298768
[math] \emptyset \subseteq A[/math] by definition. For [math] B \subseteq A [/math] we have [math] A \cap B = B [/math]

[Anonymous No.9298811]

I know how to write a proof for {14n | n ∈ N} ⊆ {7n | n ∈ N} in natural language, but is there a way I can (and probably should write it} in mathematical terms?

[Anonymous No.9298812]

>>9298786
>>9298786 <- This, or alternatively [math]\emptyset \subset A\cap\emptyset \subset \emptyset[/math], the first inclusion is what that anon said, the second comes from the fact that for any set, its intersections with other sets are always its subsets (that is, [math]A\cap B\subset A[/math] for any sets [math]A, B[/math]).

[Anonymous No.9298835]

>>9298811
Take an element of the 14n set and prove that it is an element of the 7n set.

[Anonymous No.9298836]

>>9298811
Let [math] x \in \{14n~|~n \in \mathbb{N} \} [/math]. Then there exists [math]n \in \mathbb{N} [/math] such that [math]x = 14n[/math].
Let [math] m =2n [/math], then [math]x = 7m [/math] and [math] m \in \mathbb{N} [/math].
Thus [math] x \in \{7n~|~n \in \mathbb{N} \} [/math].
Thus [math] \{14n~|~n \in \mathbb{N} \} \subseteq \{7n~|~n \in \mathbb{N} \} [/math]

[Anonymous No.9298839]

>>9298836
That's absolutely perfect, makes complete sense so I can use it to solve the rest of these too. Thanks!

[Anonymous No.9298865]

How do you faggots remember so many formulas?
I'm a pure mathfag and I'm trying to learn physics but there are a fuckton of formulas.
Or maybe I'm too brainlet for physics.

[Anonymous No.9298878]

>>9298836
I managed to all of them except for the last, which is to prove for an empty set - what's the best approach for that?

{3k + 2 | k ∈ N} ∩ {12l| l ∈ N} = (/)

[Anonymous No.9298879]

I absolutely hate science subjects, at least from my experience with the horrible pracs and badly written, open ended questions. However, I'm currently looking into medicine because I like learning about physiology and have a good memory. Also it seems to lack the shitty open ended questions that make less-related biology subjects like genetics so awful to me. How do I know if I'd like it? Does it sound like I'd like it?

I don't know what the fuck else to do at college except radiography which might actually be harder to get into and could only take a year less than premed + med school.

[Anonymous No.9298887]

>>9298878
[math] 3k+2 = 12l \Leftrightarrow 3k = 2(6l-1) [/math]
[math] 6l -1 [/math] isn't divisible by [math] 3 [/math], so there's no possibility of finding [math] k [/math] and [math] l [/math] that satisfy the equation.
Thus the set's don't share any common elements

[Anonymous No.9298888]

>>9298887
Yeah that makes sense, I thought it would be that, thanks!

[Anonymous No.9298909]

So I have run into a simple problem.
I have a bijective image F: N -> N.
If you think about convergence it would seem to make sense that

\lim _{x \to \infty} \frac{1}{f(n)}=0

since the denominator grows infinitely small resulting the expression to be equal to zero.

I have to show that the expression is what it is.
How do I show this via convergence?

[Anonymous No.9298926]

>>9298909
You gotta prove that for every [math]m \in \mathbb{N} [/math] there exists an [math]N \in \mathbb{N} [/math] such that [math] f(n)>m [/math] for all [math] n>N [/math]. The you can use [math] \varepsilon = \frac{1}{m} [/math]

[Anonymous No.9298942]

>>9298909
>>9298926
Let [math] \varepsilon > 0 [/math]. Then there exists [math]m \in \mathbb{N} [/math] such that [math] \frac{1}{m} < \varepsilon [/math].
Let [math] N = \max \{f^{-1}(1),...,f^{-1}(m) \}[/math], then [math] f(n)>m [/math] for all [math] n>N [/math].
Thus [math] \frac{1}{f(n)} <\frac{1}{m} < \varepsilon [/math] for all [math] n>N [/math]
Therefore [math] \lim _{n \to \infty} \frac{1}{f(n)}=0 [/math]

[Anonymous No.9299086]

>>9298909
>infinitely small
No such thing.

[Anonymous No.9299162]

>>9290753
How long is too long to take a pause in a certain subject?

I took all my maths and chemistry to get my bachelor in microbiology & immunity. I only took mechanics 3 years ago and never had to take physics related courses again.
Now I want to get the rest of the physics courses for an eventual Grad degree, but is a 3 year pause between courses too much?
I'm feeling like a brainlet because I can't remember anything I learnt in mechanics.

[Anonymous No.9299470]

what exactly does Eigenvalue or Eigenvector mean? I've not come across it in math, but in physics. i know how to solve Schrodinger's equation to find Eigenvalues of energy in quantum harmonic oscillators and such things , but have no idea WHAT exactly I'm finding.
could someone explain the meaning it how to visualize these terms without using the scientific language like in Wikipedia?

[Anonymous No.9299495]

>>9299470
Here:
https://www.youtube.com/watch?v=PFDu9oVAE-g

[Anonymous No.9299629]

Convolution reduces to multiplication in the frequency domain. How?

[Anonymous No.9299650]

>>9299629
https://en.wikipedia.org/wiki/Convolution_theorem

[Anonymous No.9299784]

>>9298619
Algebra. Go watch some kahn academy videos.

[Anonymous No.9299788]

How do you get good at simplifying expressions, specifically with Matrices?
I don't know where to start.

[Anonymous No.9299930]

>>9299788
You have to be more specific.