/sqt/ - Stupid Questions Thread

Old is ded

>give context
>describe your thought process if you're stuck
>try wolframalpha.com and stackexchange.com
>How To Ask Questions The Smart Way catb.org/~esr/faqs/smart-questions.html

Previous thread (Cross-thread)

Attached: 1507602209540.jpg (1218x1015, 212K)

Other urls found in this thread:

onlinegdb.com/B1eaRgVYf
gnuplot.sourceforge.net/demo/complex_trig.html
telegraph.co.uk/science/2018/03/12/dna-tests-can-predict-intelligence-scientists-show-first-time/amp/
youtu.be/ANi709MYnWg?t=7m20s
mathworld.wolfram.com/BernoulliDifferentialEquation.html
twitter.com/NSFWRedditGif

I'm trying to find concentration in litres in a less convoluted way (provided I did it right)

I have obtained 21 grams of precipitate from 300ml of a sample, and need to convert this neatly to grams per litre.

Intuitively, I'd go:
(21/300) * (1000/300), but is there a tidier way than multiplying by a fraction?

Attached: 22.jpg (500x500, 26K)

Is there a maximum AC frequency through a conductive material?

21 g / (300 mL * 1 L / 1000 mL)

>(21/300) * (1000/300)

I think you mean to write
(21/300)g/mL * (1000/1)mL/L

Don't know why you would put 300 twice in there like that.

I think if you switched the current so fast it would essentially look like a constant current of whatever the amplitude is. That's more or less true for any wave whose frequency is set super high.

>But your formula unfortunately is the same as
>(21/300) * 1000

Fuck do you mean nigga? Are you not aware that (21/300) * 1000 is the same thing as (21*1000) / 300 ?

Yes, actually this make sense.
Thank you for your help.

Why are trigonometric angles "backwards"? Is it just a prank by some ancient mathematician or is there an actual reason for why it is like that?
Pic related, left side is what we're currently using and right side is what I'm suggesting. The straight lines above the triangles are supposed to be vectors going in the same direction with each other and how they're angled to each other.

Attached: angles.png (929x935, 24K)

I like the way you think.
I had a similar thought process when i was young mostly supported by circles also having 360 degrees. This doesn't make any sense with how we do things currently but lines up perfectly with your method

what do you mean by "essentially look like"?

Take a sin wave (imagine a slinky), then compress this wave until it's so close together that you get a constant line right at the amplitude. The alternating current becomes a constant current.

That's just the external angle

I actually didn't realize that until you pointed it out. That answer is good enough for me, thanks.

Trying to do a c++ exercise to take a linked list and return a list containing only the even values .At the point where I want to run it to check how/if it's doing what I expect but I'm getting a type error and I can't seem to figure out why. Any chance someone could shed some light on it?

onlinegdb.com/B1eaRgVYf

The fuck is wrong with you

You're not the first person to ask me that and I'm sure you won't be the last one either.

no it fucking doesn't

When you increase the frequency super high yeah

What's stopping physicists from redefining current in the other direction?

it may be minor, and not fundamentally affect the mathematics, but it's ludicrous that we just keep going deeper and deeper in to that hole. We switched to SI units, we redefined potentials in thermodynamics. So how hard can it be to reformulate current in the opposite direction.

Because positive and negative charges are arbitrary anyway, and the physical movement of electrons is useless information.

But if physics aims to be an accurate description of what's actually going, surely taking one sign convention in one context, and then flipping is another such that it implies something entirely different is a pointless inaccuracy.

What should I know about maths when doing a Masters in chemistry. I have the feeling that my maths is lacking.

At least you didn't make a thread about it. You are already better than 60% of Veeky Forums

Attached: 1515361365583.png (729x638, 154K)

From previous:

If we consider an arbitrary real number defined as the equivalence class of Cauchy sequences, is this set of equivalent sets uncountable or countable? Are there any simple proofs of this?

Ask your professor. Or look up the mathematical requirements of each course you are going to take. It's not that hard.

even_nodes is a function
printList expects a list

Speaking of Geometry/Trigonometry, I have this gem:

"Given two lines a and b. Prove, that any line, crossing a, crosses b too, thus, a || b"

I saw the answer and it kinda make sense but isn't a triangle (formed by intersection of 3 lines) would be a valid special case here? I mean, sure, the condition does not say if a and b are crossing or not, so it is up to any interpretation and thus a can cross b and c can cross both thus a cannot be || to b

We simplified it by dividing nominator (each additive) and nominator by "y2"

can someone tell me how the heck you get from

[math] \frac{4*x^2*y^3 + 3*y^2}{10y^2} [/math]

to

[math] \frac{4*x^2*y + 3}{10} [/math]

instead of

[math] \frac{4*x^2*y^3 + 3}{10} [/math]

? where the hell did the y^3 go

"positive" has no meaning other than "not negative" and negative has no meaning other than "not positive"

It literally doesn't matter unless you show that there is some way to distinguish these two in some unsymmetric way. It's like asking why we make the x-axis of a graph positive to the right instead of left. We just picked one. It doesn't mean anything.

division and multiplication distribute over addition

Attached: Penguins.jpg (1024x768, 760K)

>each additive
thanks

What kind of jobs can I get with a masters in data science? Data analyst? Any machine learning work?
I feel like I'm about to fall into one huge meme

I assume you want those sequences to be rationals, but even then I think it's fairly easy to show that there are at least continuum many such sequences.
Consider a sequence [math]A=\{a_n\}[/math] of rationals that converge to [math]\alpha[/math].
Now consider a sequence [math]B=\{b_n\}, \forall b_i\in \{0,1\}[/math], I will define [math]A'_B=\{a'_n\}[/math] as [math]a'_1=a_1[/math], if [math]a'_k=a_n[/math], then [math]a'_{k+1}=a_n[/math] if [math]b_k=0, a'_{k+1}=a_{n+1}[/math] if [math]b_k=1[/math], where by equal I mean it's defined by that member of the original sequence.
Basically in each step I'm deciding whether to stay in place or not according to [math]B[/math], it's easy to see that these new sequences always converge to the same number as long as there are infinitely many 1's in the sequence. Note that these are the real numbers in [math](0,1][/math] in base two, where if you can represent a number with two sequences, you always choose the one that ends in repeating 1's. There are, of course, continuum many real numbers in that interval, so I could construct continuum many different sequences, if for example I require the original's terms to all be different from each other.

Ahh interesting construction! Thanks, that's really clear and interesting. In my mind I had only thought about the finite number of leading terms that may differ, I hadn't considered the notion of rates of convergence at all. Your clever "delayed convergence" map makes it clear.

You're welcome, but I realized an equivalent but maybe cleaner description would be [math]S_n=\sum_{k=1}^{n}b_k, a'_n=a_{S_n}[/math]

I'm trying to see how I can plot complex numbers, and I came across "domain coloring" which looks like a pretty neat way to plot things.
Problem is, I have no idea how to actually do this in something like Matlab.
Any ideas?

Attached: Domain Coloring .png (1266x1432, 684K)

my butthole is bleeding, am I going to die?

just learn an actual programming language

you probably have hemorrhoids just buy some tucks and stop eating fucking garbage

10 cups of green leafy vegetables or cruciferous vegetables a day

stop eating sugar and carbs

Okay that's fair.
I just said matlab because it's kind of easy to plot with it.
I know C/C++, Python, a couple others, any ones you recommend I work with?

>I just said matlab because it's kind of easy to plot with it.
I'd be surprised if it didn't already have this functionality.

You could also just use gnuplot.
gnuplot.sourceforge.net/demo/complex_trig.html

e^Mt = PAP^-1
How do i use this to solve systems of differential equations with initial conditions? Is it even necessary? I have a really bad time understanding solving initial conditions and non homogeneous equations. Somebody save me my final is in 2 days.

>stop eating slow sugars
Guaranteed shit-tier attention span.

I don't understand this proof. How does the expression above the two points circled imply the RREF of A is either the identity matrix or has a final row of zeroes? It feels like they made an unjustified leap with the part circled. Or they're redefining the proof to only encompass certain n x n matrices A and not all.

Attached: product rule.png (1057x739, 132K)

That's because A is a square matrix. There are only those two possiblilities for the RREF of a square matrix.

>>give context
I live in Cape Town which has its worst drought in years. Some people use borehole water for irrigation.
At a social event the discussion went to the use of borehole water and what happens when the water is not replaced and the water table drops.

The statement was made by my uncle and aunt that the water will eventually be replaced by sea water if the rain does not bring the water back to the normal level. their explanation was "it's physics".

>question
Are they right is it physics?
My thought is that the water cant be replaced by sea water because that would imply the sea water "flows" upstream to fill the water table.
If I have to report to them that they are wrong they will require sources so please help a brainlet user out.

Attached: 1408364285594.jpg (300x300, 24K)

the water below ground is not necessarily above sea level, though it is my understanding that groundwater is generally a function of water from other sources like snowmelt (good) and rain (shitty).

If it only came from the ocean filtering through rocks you are correct that it cannot be above sea level without weird shit happening underground.

Thanks, because they just state it is because of physics, which as anyone on Veeky Forums (hopefully) will tell you is not really a good answer.
I'd appreciate if anyone else could also give some insight.

freshwater can sit on top of saltwater because of the difference in densities, if the pressure around the freshwater and saltwater boundary is in equilibrium then the saltwater will not rise, but if the freshwater that sits on top of the saltwater is depleted, and the pressure of the saltwater at the boundary remains constant, then the saltwater will rise since there will be a pressure differential at the boundary in favor of the saltwater.

essentially the freshwater is pushing down on the saltwater, but if we remove the freshwater, there is nothing to push the saltwater down anymore so it will rise.

but as said, it would be ridiculous to assume that the saltwater will rise above sea level

I don't really know much of anything to do with groundwater, just applying some concepts of physics 1

So one can assume that there may be some salt water in the existing water table provided that it is below sea level. If the water gets depleted it could fill with sea water until sea level?

>So one can assume that there may be some salt water in the existing water table provided that it is below sea level
I'd say that's pretty reasonable, probably lower salinity levels the higher up and further inland it is

>If the water gets depleted it could fill with sea water until sea level?
I would imagine that the salinity of the water would increase as more water is depleted, but the water level would stay at roughly the same height since it is replaced with seawater

I could see some long lasting consequences of letting the salinity increase in the higher level groundwater, once the salt gets in there, it would most likely stay there for a pretty long time

>telegraph.co.uk/science/2018/03/12/dna-tests-can-predict-intelligence-scientists-show-first-time/amp/
Is this legit? how can one use this knowledge to improve a grown individual's mental performance? I don't wanna be brainlet anymore.

Attached: 1513909310231.png (645x729, 56K)

What concentration of chemistry?

For an undergrad you need up to diff EQ anyway.

i want to take a math theory / history of math class next semester
what should i expect
i'm really interested in the philosophical aspect of math

Attached: 1509297373080.jpg (699x485, 69K)

>Stupid Questions Thread
How do magnets exert force in the direction PERPENDICULAR to the motion of charged particles?

Attached: TRINITY___Jimmies.jpg (600x337, 58K)

Christ, you're probably one of those faggots who makes a big fuss about Pluto being/not being a planet.

What the fuck is going on
I understood the jump from 1 to 2, but then I don't really know how to get the angle

Attached: wtf.png (294x111, 7K)

Hey lads can you see if I did anything wrong in my proof? Did I assume too much or is it just plain silly? Looking to know if I need to fix it. Thanks in advance

Attached: 1e0e97f35319ae08127347f05cbf63a1.png (587x203, 39K)

Whoops! Meant to have f(x) is an element of B\f(c) not the other way around on the third line

you can use phasors to turn the equation into one that is easily solved with a calculator
[eqn] A\sin\phi - B\cos\phi = \sqrt{A^2+B^2}\sin(\phi-\arctan(\frac{B}{A})) [/eqn]
you could also use some trig identities to do something similar but as I recall it's quite the hassle

Thank you
>phasors
Never head about it, gonna check it now

Does anyone have any tips on how to do and keep track of long tedious calculations? I'm doing inverse matrices through matrix of minors but I keep fucking it up because of minor errors. The actual method is OK, the end matrix looks similar to the right answer, the numbers are just off by a bit because somewhere in that mess I added something wrong.

Something to do with special relativity and the fact that charges move super duper fast.

that's messed up right

Attached: vlcsnap-2017-09-25-06h17m50s320.png (1280x720, 849K)

Carbon dating

If the rationale behind carbon dating is that dead organisms do not take in anymore new carbon which replenishes that organism's supply of carbon 14, then that must mean that carbon 14 is produced in some small part of the environment.

So what part of the environment contains all the carbon 14, and how does that end up in all living organisms?

Is there other equations like this? This is handy as fuck

>So what part of the environment contains all the carbon 14, and how does that end up in all living organisms?
The air. Breathing.

Is this a troll post?

Cosmic radiation converts N-14 to C-14, which reacts with oxygen to form CO2.

Does anyone have a good reference for information on regularization of Eisenstein sums?
In particular, I want to know a good way regularize

[eqn]
\sum_{\substack{(m,n)\neq (0,0)\\ (m,n)\neq(m_0,n_0)}} {1 \over m + n \tau}
[/eqn]
with [math](m,n)[/math] taking values on an integer lattice and [math]\tau [/math] the complex modular parameter (not very important here).

Feels like college is sapping away my youth, and I was planning to do med school but the idea of doing nothing but working and studying until I'm nearly 30 is a grim prospect. Is med really worth it in terms of the money when I can do other hospital shit with less than half the study time? The fact that they drag shit out for so long makes me think it's more of a cash grab, plus doctors seem to make shit money for their first years of actual work despite the god complexes.

Why does
[math]y’ = y^2 - y[/math]
yield
[math]y = \frac{1}{1+ce^x}[/math]
and not
[math]y = \frac{1}{1-ce^x}[/math]?

we can add any number of sinusoidal functions together in a similar manner as long as they have the same angular frequency. By representing the functions as phasors, the problem turns into simple vector addition.
We can therefor make a general formula for adding two functions as follows
[eqn] A\sin(\omega t+\phi_a)+B\sin(\omega t+\phi_b)=C\sin(\omega t+\phi_c) \\\
C=\sqrt{A^2+AB\cos\theta+B^2} \\\
\phi_c=\phi_a+\arctan\frac{B\sin\theta}{A+B\cos\theta} \\\
\theta =\phi_b-\phi_a [/eqn]
Since the cosine function is just a sine fuction with a phase of 90 degrees, the formula simplifies rather nicely as in the previous example.

Attached: Sumafasores.gif (300x593, 617K)

Can't you just use the Pythagorean theorem?

Attached: hqdefault.jpg (480x360, 9K)

is my discrete mathematics textbook wrong? pretty sure -1 > -2 lol

Attached: Screen Shot 2018-03-13 at 5.54.19 pm.png (386x44, 10K)

isn't it >= cross there?

Why is there are Zero marked for carbonic acid?
youtu.be/ANi709MYnWg?t=7m20s

Attached: nimetön.png (861x521, 301K)

Just to show that it's neither positively nor negatively charged. It's superfluous.

I'd assume because the constant is undefined regardless, so you can expect it to be negative or positive.

mathworld.wolfram.com/BernoulliDifferentialEquation.html

What are some real risks of activity in space or other near vacuum? Like in the movies they cant decide between exploding or freezing. Also I heard losing heat is an issue in space but then why is it described as cold? Also I heard friction welds can be a problem but I don't really know what that means.

Attached: 1512143218473.png (379x545, 457K)

It's like writing 1x, you don't need to include the '1' because it's common knowledge that the one exists. The same thing goes for chemically neutral compounds. You can write that the charge is equal to zero, but most of the time it is neglected because it is common knowledge that if you don't write the charge that it is neutral (hence 0).

Your body stays together because there is a strong pressure caused by earth's atmosphere that presses on everything at the surface. When you take away this pressure your eyes can pop out and your orifices can pull out backwards.

Even though space is cold, your blood will boil rather than freeze. This is because there is no pressure to keep the blood compressed into a solid, so it just phases out like a gas.

Your skin will freeze, but you will also swell up (I don't want to say explode because it's not an explosion).

>When you take away this pressure your eyes can pop out and your orifices can pull out backwards.
The difference in pressure really isn't that extreme. Your eyes will likely boil away well before the vacuum can suck them out.

>Also I heard losing heat is an issue in space but then why is it described as cold?
Losing heat is an issue because there's no matter around to absorb it. Space itself isn't cold, per se, but the only real source of heat in deep space is the cosmic microwave background - which works out to about 3 Kelvin, or -270 degrees Celsius. If you experienced that temperature through Earth's atmosphere, you would freeze instantly due to the air's conductivity. In space, there is zero conductivity, so things just tend to "lose heat" because there's nothing (besides CMB) pushing them towards a temperature equilibrium.

What's good software for plotting algebraic curves, in particular in a projective space (real/complex namely)?

(a+b)/c=(a/c)+(a/b)

a=(4*(x^2))*(y^3)
b=3*(y^2)
c=10*(y^2)

So from your step 1 we get
(a+b)/c
=a/c+a/b
=((4*(x^2))*(y^3))/(10*(y^2))+((3*(y^2))/(10*(y^2)))
=(((4*(x^2))*y)/10)+(3/10)
=(4*(x^2)*y+3)/10

That's not exactly helpful.

Thanks, user. I think that's it.

> What are some real risks of activity in space or other near vacuum?
Suffocation, hyperthermia.

> Like in the movies they cant decide between exploding or freezing.
Movies don't care about realism.

The "freezing" part is probably because someone with no scientific background heard "space is cold" and assumes that means that you'd freeze.

Without life-support, you'd die from overheating. Space is a vacuum, which doesn't conduct or convect heat, and at body temperature radiation alone isn't sufficient to get rid of body heat.

thanks user

?

Attached: 0EIjt4g_d.jpg (640x480, 16K)

Yeah? The point that the question was worded poorly and states that if there us a line c crossing a and b then a || b. Which may not be the case.

The "proper" solution is: let's assume c crosses a but does not cross b - that means c can be || b but this is against the condition of the question (if c crosses a then it later crosses b). Let's assume c does not cross a - but we can't, because condition explicitly states c crosses a.

It is kinda retarded wording and tricky question.

If a crosses b, that means they aren’t parallel.

>if there us a line c crossing a and b then a || b.
It’s stating the inverse. If a||b, any line crossing a must cross b; that doesn’t mean that one line overlapping two others can indicate whether they are parallel.

>If a crosses b, that means they aren’t parallel.
Yes but the question does not say anything about it, it just says given 2 liens a and b.
I agree, it is can be possible which is why I said what I said here: Fair enough, it can be inverted, but original question still worded poorly.

I know basically nothing about engineering or CAD. What software would be used to model cryogenic distillation of gasses? Would need to be able to handle pressure, temperature, phase changes, etc. Does such a thing even exist as a single software suite?

Attached: air[1].jpg (957x606, 123K)

the mathworld definition of an augmenting path is wrong, right?

Attached: aug.png (719x82, 6K)

I have the system of differential equations:

[math]
\dot{x_1} = v_1
\\ \dot{x_2} = v_2\\
m_1 \dot{v}_1 = \underbrace{ \frac{-q_1 q_2}{(x_1-x_2)^2} + F_1(t)}_{\text{A}}\\
m_2 \dot{v}_2 = \underbrace{ \frac{-q_1 q_2}{(x_1-x_2)^2} + F_2(t)}_{\text{B}}\\
[/math]

I've been taught that to solve this, I should put this in terms of a linear system of equations, then plug it into an ODE Solver like MATLAB's ode45().
My question is, how would I solve this one? I can't see how I would place it in terms of matrix multiplications of the form:
[math]
\vec{y'}(t) = D \cdot \vec{y}(t)\\

y(t) = [x_1, \quad, x_2, \quad v_1 = \dot{x_1}, \quad v_2 = \dot{x_2}]\\
[/math]

can a nonbrainlet help me out

Attached: lbv4Hqr_d.jpg (640x384, 21K)