/sqt/ fuck this fucking level 49 edition

[Anonymous No.10412555]

This is the thread for all stupid/simple math/science-related questions that you should have learned during high school or undergrad. All slightly science-stuff that really doesn't deserve its own thread otherwise goes here-LIKE THIS FUCKING CHILDREN'S MATH PUZZLE THAT I CAN'T SOLVE. Can /sqt/ solve it and post the result?

Second-to last level of the game: start game, hit the back button once, select level 49 (second-to-last, the game lets you play any level right at the start). No, the solution isn't online so don't even bother suggesting that, someone posted levels 1-36 only:

https://armorgames.com/play/18529/chain-sums

The object of the level is to move the tiles until the linked sums partition into 17, 20 and 36. Each tile has rigid connectors which automatically connect to adjacent connectors when placed adjacently, starting a sum going. Tiles can only be permuted/translated on a rigid grid (5x3 in this case), they cannot be rotated. Further, chains do not have to be "closed"; as long as you have all chains with the right partitioned sums that aren't connected to each other, they can have dangling/loose ends. There is an example of another level which can be solved with this.

[Anonymous No.10412560]

>>10412555
The answer is trivial :^)

[Anonymous No.10413588]

at least link the new thread in the old one you inbred degenerate brown skin.

[Anonymous No.10413895]

>>10412555
>LIKE THIS FUCKING CHILDREN'S MATH PUZZLE THAT I CAN'T SOLVE
>CHILDREN'S
nice children you got there m8

https://en.wikipedia.org/wiki/Subset_sum_problem
>NP-complete
+
https://en.wikipedia.org/wiki/Routing_(electronic_design_automation)
>Almost every problem associated with routing is known to be intractable.
EDA (or FPGA) Place & Route has been proven NP hard.

[Anonymous No.10415330]

What is the purpose of harmony? Why playing different notes at the same time sounds better than playing just one note? Aren't harmony and overtones the same? Couldn't you build an instrument that had the same overtones as a harmony?

[Anonymous No.10415358]

>>10415330
That question is even too stupid to be answered.

[Anonymous No.10415373]

>>10415358
how come?

[Anonymous No.10415960]

Can anyone help me understand this? Some points, clearly visible guards are guards that have 360 visibility range but cant see past vertexes. G(n) = max number of guards required from the set of all minimum amount required guards to guard all n-sided Polygons.

[Anonymous No.10415961]

>>10415960
Part 2

[Anonymous No.10415996]

>>10415330
polyphonic harmony is much simpler than the overtone series that defines the timbre of a specific pitched sound. You could make an instrument that plays this whole sound at the touch of a button -- for example an instrument that plays samples -- but there are two problems with such an approach. 1) polyphonic voice leading requires different voicings for each chord, so your instrument would require too many keys 2) it is essentially impossible to achieve this kind of timbral variation with an acoustic instrument.
you may be interested in an instrument is called a Shrutibox. it will give you an idea of what overtone rich timbres sound like.

[Anonymous No.10416070]

im reading a paper about generating gear teeth profiles numerically. i cant seem to figure out wtf "inv(x)" is supposed to mean in this context.

[Anonymous No.10416077]

>>10416070
heres one of sample calculation using the formulas.
inv(v) = PI * mb / z.
in the example this yields:
inv(v) = 0.17.
wtf is the "inv(v)" function that yields 42.14 degrees?

[Anonymous No.10416096]

Is multivariable calculus considered a pretty difficult thing among most people?
When I was studying computer engineering for a while, most people dreaded it but was that just at my school or perhaps only among non-mathematicians?
As I am not a mathematician I can only compare it to linear algebra and high school math and the beginning of it doesn't seem too bad to me.

[Anonymous No.10416107]

>>10416096
in my experience, the hardest part of any jump from single to multiple variables (or from 2d to 3d and up) is that any shortcomings you had will be multiplied.
so if you had some problems with calculus but managed to pass, multivariable calculus will bend you over the table. if you understood everything from calculus, you should be just fine. the calculations are the same, its just way more of them.

[Anonymous No.10416139]

>>10416107
Yeah that's a bit what it seems like to me too. I got a pretty thurough understanding in single variable so this doesn't seem too bad yet.
Have you studied more mathematics later and can compare the difficulty to those later subjects too?

[Anonymous No.10416140]

>>10416096
>>10416107
I'm not sure if this is just what I've learned so far but I found Multivariable calc to be a natural extension and parameterization + vector notation make everything much simpler. They didn't make me do any series in that class either which I found trickier than stuff like triple integrals

[Anonymous No.10416147]

>>10416139
no, i didnt get much further in higher math than multivariable calculus.
as far as i remember, the hardest subject in math i had to take was linear algebra.
i did have some troubles jumping from 2d to 3d robotics (its mostly linear algebra there). i realized i had a lot of problems with linear algebra that i had to patch before moving on to 3d space.

[Anonymous No.10416178]

>>10416070
>>10416077
I don't think inv(v) = 42.14, I think v = 42.14. Inv is probably just the same thing in radians, considering the additional factor of pi in equation 4a. Look back in the paper to see where "z" is defined.

What a fucking mess though lol

[Anonymous No.10416199]

>>10416178
yeah, i was a bit unclear:
inv(v) = 0.17
v = 42.14 degrees.
z is defined in the table (second pic), its the number of teeth.
0.17 radians is ~9.7 degrees. i tried complimentary angles, inverse angles, inverse trig functions, simply inverse (1/x), etc. this shit doesnt make any sense and "inv(x)" isnt defined anywhere in the paper.

[Anonymous No.10416385]

>>10416070
>>10416077
ffs, I finally managed to track down what "inv(x)" here means, although I'm not sure I understand it fully.
from another paper on the same topic:
inv(v) = tan(v) - v.

[Anonymous No.10416545]

In some of my classes atm we are proving that there exists an example to a statement because the probability of any element of the set satisfying the condition is greater than 1.

I think I see why this works, but it seems a bit iffy to me. Is this justified?

[Anonymous No.10416580]

[math]m·g·h=m·g·h+1/2·m·v^2[/math]
[math]g·h_1=g·h_2+1/2·v_1^2[/math]
Can I keep one of the gs without getting rid of the other in order to get -g?

[Anonymous No.10416618]

>>10416580
Or would it become 2g?

[Anonymous No.10416843]

>>10416096
I hated multivariable, the problems and so on weren't very difficult but I couldn't deal with not understanding the theorems. I didn't understand why Jacobians worked, I didn't understand why Stokes theorem worked, etc. etc. and I found that frustrating as hell.

[Anonymous No.10418077]

I'm looking to study physics. Is the University of Utah worth considering?

[Anonymous No.10418127]

>>10418077
Just do engineering

[Anonymous No.10418152]

>>10418127
I don't actually want to be an engineer

[Anonymous No.10418153]

>>10418152
Neither do engineers

[Anonymous No.10418176]

>>10412555

learning basic capacitor stuff, dealing with series/parallel hybrids.

How do you find individual charges of capacitors??? I look at solutions and they use what appear to be random ratios between known/solved capacitance. Please help

[Anonymous No.10419014]

>>10418176
1. Q=C*V
2. For capacitors in parallel, the voltage on each is the same.
3. For capacitors in series, the amount of charge on each is the same. And equal to the amount of charge moved through the chain (i.e. the total charge of a series chain is equal to the charge on any one capacitor). Q=integral I dt, and I is equal along the chain.

Bear in mind that the net charge on a capacitor is always zero: the positive charge on one plate exactly cancels the negative charge on the other. Capacitors don't store charge in the sense that you're filling them up with electrons, but in the sense that you add electrons to one plate and remove them from the other. So when you have capacitors in series, the charge that goes out of one goes into the next.

A corollary of points 1 and 3 is that capacitors in series form a voltage divider where the voltage ratios are in inverse proportion to the capacitance ratios. Q1=Q2=Q3
=> C1*V1=C2*V2=C3*V3
=> V1=V1*C1/C1,V2=V1*C1/C2,V3=V1*C1/C3
=> V1+V2+V3=V1*C1*((1/C1)+(1/C2)+(1/C3))
=> V1/(V1+V2+v3)=(1/C1)/((1/C1)+(1/C2)+(1/C3)).

[Anonymous No.10419015]

>>10412555
How2getsmarts

[Anonymous No.10419145]

>>10416096
Some things aren't as intuitive as they are in univariable calculus, but it's not that bad. As with most things, you just need to take your time to internalize and understand them well.
>>10416580
Assuming the second line follows somehow from the first, you'd get
[math]gh_1-gh_2=\frac 1 2 v_1^2[/math]
[math]g(h_1-h_2)=\frac 1 2 v_1^2[/math]
[math]2g(h_1-h_2)=v_1^2[/math]
[math]v_1 = \sqrt{2g(h_1-h_2)}[/math] (a typical sort of answer in energy problems)

[Anonymous No.10419294]

can someone explain why Kg is a standard SI unit instead of, you know, g? is it because people would confuse it with g for gravity or something?

[Anonymous No.10419547]

so I want to make a graph on geogebra
the problem is that i need to graph a telephone subscription. the constant monthly price is 10 dollars, and for every minute you pay 0.1 dollars. however, the first 100 minutes are free of charge. how do i graph it?
i know the f(x)=0.1x + 100 part, but how do i make it so that the first 100 minutes are a straight line?

[Anonymous No.10419637]

In the Glicko rating algorithm, does it make any difference at all if you calculate x matches one by one vs calculating them in one "batch"?

I'm looking for an implementation library of it and some use either approach; I don't want to use one that's incorrect.

[Anonymous No.10419665]

>>10419294
Because Newton.

[Anonymous No.10419737]

I have two intervals [math][a; b], [c; d][/math] with [math]a \lt c \lt b \lt d[/math]. I want to combine them into almost disjoint intervals (only borders can touch), that is [math][a; c], [c; b], [b; d][/math]. Is there a set-theoretic notation that can easily express this for me?

[Anonymous No.10419738]

>>10416843
>I couldn't deal with not understanding the theorems
Yeah, doing maths without the proofs and proper understanding isn't math

[Anonymous No.10419770]

>>10412555
Can prostate orgasms cause prostate cancer?

[Anonymous No.10421123]

Why is the fire in this video invisible? https://www.youtube.com/watch?v=Ku7TdLeEGsQ
Narrator says it's because the fuel is alcohol. But in videos like this https://www.youtube.com/watch?v=6B6yqrtcA7M you can see the flames of burning alcohol

[Anonymous No.10421258]

>>10419737
[math][a,b]\setminus[c,d], [a,b]\cap[c,d][/math] and [math][c,d]\setminus[a,b][/math]. (Some prefer to write [math]A-B[/math] rather than [math]A\setminusB[/math].) But I think that's uglier than writing out the actual intervals.

[Anonymous No.10421266]

>>10421258
welp, I fucked up not only my LaTeX but my logic as well — [math][a,b]\setminus[c,d]=[a,b)[/math]. Yeah, just write out the actual intervals.

[Anonymous No.10421460]

>>10419294
The original metric system was centimetre-gram-second (CGS). The SI metre-kilogram-second (MKS) took over post-WW2. The use of the kilogram as the base unit is probably related to it being easier to maintain and measure a kilogram prototype than a gram prototype (a smaller prototype has a larger ratio of surface area to volume, which would exacerbate issues with contamination).

[Anonymous No.10421484]

If anybody knows circuits and electronics and the like, pls help. I am unfortunately retarded and can barely understand what the fuck I'm doing.

[Anonymous No.10421503]

>>10421484
Well i guess it mighthelp to clarify what i need help on, huh?? I need to find the resistance at R5, but I have no idea how to do it when all I have is the voltage. How do I get the current at R5 as well? I suspect that the current listed might have something to do with it (2mA by R1 and 12mA for total current) but i just... am not finding anything in my notes or anything helpful in the information sheet.

[Anonymous No.10421616]

>>10419547
Look into graphing piecewise functions

[Anonymous No.10421627]

>>10421484
What's it actually asking?

If A is an ammeter reading 2mA, then the battery voltage is 50V (=(10kΩ+15kΩ)*2mA). So that's 2mA through R1,R2, 50V/12.5kΩ=4mA through R3, 50V/10kΩ=5mA through R4, for 11mA in total. If the total current from the battery is 12mA, then you have 1mA through R5 which means R5=50V/1mA=50kΩ. And the total circuit resistance is 50V/12mA=4166.66...Ω. Power consumption is 50V*12mA=0.6W.

So I think the answers are: 50V, 50kΩ, 4167Ω, 4mA, 5mA, 0.6W.

[Anonymous No.10421710]

Anyone willing to solve/help me with these organic chemistry problems? Will pay via paypal.

[Anonymous No.10422362]

>>10412555
https://techtv.mit.edu/videos/dbd078f356ed4fcca043eea1d8598a08/

I found this video of candles inside a rotating dome
I understand the tilt effect they describe
but I don't understand why the central candle's flame grows so much longer
I considered falling air density due to centrifugal force pushing the air to the edges

[Anonymous No.10422439]

>>10421123
Google dude

[Anonymous No.10422725]

I graduate with my bachelors in December 2019, and recently became interested in grad school. How fucked am I if I have no research experience yet? I have a good gpa and gre should be easy, but how do i get into some experience for my resume? Ive had one internship (unrelated to grad school specialty) and may have a relevant one this summer if i dont do summer research instead

[Anonymous No.10422743]

>>10421627
Oh wow. I didn't get the chance to respond, but you're right! Thank you so much!!!

[Anonymous No.10422903]

Is this right?
The derivative of 6te^(-5t) = -(30t-6)e^(-5t)
Then I multiplied that by e^(-st) and integrated from 0 to infinity.

[Anonymous No.10422932]

uh guys

[Anonymous No.10423046]

Are there any cosmologists here?
I understand the definition of luminosity distance as
[math] d_L = \sqrt{\frac{L}{4\pi F}} [/math]

but how does one get

[math] d_L = c(1+z)\int_0^z\frac{dz'}{H(z)} [/math]

(for a flat universe)

?

[Anonymous No.10423128]

>>10422932
It's wrong. Show your work. This is literally just 2 babby integrals

[Anonymous No.10423130]

>>10421484
How do you suck at drawing lines? Holy shit it's so bad, it's worse than a 1st graders

[Anonymous No.10423135]

>>10419021
>>10419032
The other thread is dying, and I never got an serious reply. I'll post this here

[Anonymous No.10423281]

>>10416096
I thought it was pretty easy. I cheated my way through Calc 1-2 and ended up with an A in calc 3, this time actually trying.

[Anonymous No.10423348]

Why do people on this board meme about math requiring little memorization even though there are lots of theorems that I am apparently supposed to memorize? Or am I just suppose to 'remember' my proofs of them?

[Anonymous No.10423546]

>>10422903
> Is this right?
Yes. Note that you can skip the differentiation step. The Laplace transform of 6te^(-5t) is 6/(s+5)^2, and L{f'(t)}=s*L{f(t)}-f(0).

Also: L{t^n*e^kt}=n!/(s-k)^(n+1). This is worth memorising, including the first few specific cases L{e^kt}=1/(s-k), L{te^kt}=1/(s-k)^2, L{t^2e^kt}=2/(s-k)^3, as all linear ODEs have solutions involving only these terms.

Most practical use of the Laplace transform involves converting a linear ODE to the s-domain (giving a rational function in s), finding the roots of the denominator (poles), partial fraction expansion to get a bunch of a/(s-k)^n terms, then the inverse transform on the individual terms to get a*t^n*e^kt terms (where k is often complex).

[Anonymous No.10423564]

>>10422725
someone throw a nigga a bone

[Anonymous No.10423660]

I have something that transitions to one of three states. It should trasition to A with a 40% chance, to B with 35% chance and C with 25%.
Lets say we have a case where state A is not getting picked, how do I calculate the probability that it will be B or C?

[Anonymous No.10423664]

How do you prove the boundary of a boundary of a set is contained in the boundary of the set using only the definition involving neighborhoods? It seems it shouldn't be that difficult but I'm getting no where.

[Anonymous No.10423682]

>>10423660
You have two events with relative probabilities of 35 and 25. So 35/60 B, 25/60 C.
Now this is assuming you haven't created a situation where the probability of transitioning to A is 0, you don't know anything about the probabilities of transitioning to state B or C then.

[Anonymous No.10423694]

For how many rational values of x is P(x) = |x^2 - 28x + 160| a prime number?

[Anonymous No.10423730]

>>10423682
Thanks, makes sense.

[Anonymous No.10423743]

>>10423694

Remark 1: we assume a universe of discourse among the reals, to be further restricted for discussion when appropriate.
Remark 2: the inner expression, the basic polynomial, is a quadratic, which when graphically expressed, gives a parabola, shooting up.
Remark 3: the effect of the enclosing absolute value notation upon that quadratic is to vertically flip such-and-such (a non-empty interval) above the x-axis. So the thingy maps from the reals onto the nonpositives (touching zero twice), and the image thus hits all primes, a subset of strictly positive integers entailed in the nonpositive reals.

Remark 4: The above three remarks dance around the problem. Let us restate the problem in view of the above, with a view toward solving the problem. WLOG (interpreting the problem's intent): completely find/classify/identify all rationals in the domain/preimage such that a prime poops out in the image. Clearly every prime is in the image, but non-example pairs would be those with irrational preimage -> prime image (do such exist?)

Remark 5: the thingy is obviously even, so you can flip it horizontally too. so you get your primes-images twice etc.

Remark 6: The rest is left to whomever may be interested.

[Anonymous No.10423745]

so im taking this diffeq class and i havent been to the last few lectures. whos this homo genius guy the prof keeps talking about?

[Anonymous No.10423754]

>>10423694
suppose the stuff in the abs is positive for now
if P(x) = p prime, then x2 - 28x + 160 - p = 0
the roots of this polynomial are:

x_1/2 = 14 +- sqrt(142 - 160 + p)

these are rational iff 142 - 160 + p is a positive square number.
now we have check if there are any primes so p + 16 is square.

second case, the stuff in the abs is negative
P(x) = p prime, so -x2 + 28x - 160 - p = 0
x_1/2 = 14 +- sqrt(142 + 160 + p)
again, check if 356 + p is square

one has to additionally check that for each found prime the stuff inside the abs actually has the correct sign for the case. this probably means it cuts of a finite amount of the first case and almost all of the second. but i have not yet proven that.

[Anonymous No.10423757]

>>10423754
god damn 4chan formating can't differentiate between x2 and x2

[Anonymous No.10423758]

>>10415996
based and music theory pilled. i'm currently learning about augmented sixths (i.e., Italian, French, and German).

[Anonymous No.10423817]

>>10423758
any opinion in their natural just intonation spelling? It seems difficult to interpret them if the sixth isn't their root. In particular the french seventh seems like a fundamentally septimal chord to me...

[Anonymous No.10423822]

The notation on the right is set-builder notation. Does the notation on the left have a name?

[Anonymous No.10423894]

>>10412555
I wasted too much fucking time on this

[Anonymous No.10424154]

How do you figure out the speed of an ion moving through an electrical field when it goes from one potential to another using mass, initial speed and a potential at point A and another at point B?

[Anonymous No.10424199]

>>10423822
No; it's just a binary set operation whose definition is the set on the right.

[Anonymous No.10424336]

>>10424154
Potential energy = charge * potential.
Kinetic energy = (1/2) * mass * speed^2.
Their sum remains constant.

[Anonymous No.10424421]

>>10424336
Thanks, I got one question out of two right but I have no way of knowing which one it was.

[Anonymous No.10424766]

Any advice for dealing with bastard professors? I'm in freshman chemistry but the professor is an Asian dude with an accent so thick I can barely understand him half the time, and he grades so harshly that the average for class assignments is like 28%.

Should I just learn how to do all the nitpicky bullshit to make him happy? He doesn't do partial credit, if you make one microscopic error the entire thing is wrong, like using a line with marks for a graph instead of just the marks without the line.

[Anonymous No.10424892]

How do i integrate 1/v dt where v is velocity?

[Anonymous No.10425090]

>>10412555
This shit is so easy. You are a fucking retard.

[Anonymous No.10425162]

>>10419770
they actually help prevent it

[Anonymous No.10425349]

>>10425090

I don't even care about the insult or that you're an apparent phone poster. Thank you for posting that, god damn.

[Anonymous No.10425373]

>>10425349
lurk more because youre clearly too incompetent to recognize a phoneposter which I am not

also fuck you for making me feel bad for being rude

[Anonymous No.10425376]

>>10422725
What uni, what area, you may not be fucked if you aren't aiming too high.

[Anonymous No.10425519]

can convolution be possible?

[Anonymous No.10425529]

>>10424892
log(abs(v)) + C where log is the natural logarithm and C is a constant. This can be proved by using integration by parts.

[Anonymous No.10425572]

I have a square with known vertex points. Let's say I deform the square by moving all of the vertices to some new coordinates. The stretched object is a polygon with 4 vertices. Is there an easy way to construct a mapping which takes some point inside the original square and outputs the coordinates of this point in the new polygon?

[Anonymous No.10425847]

>>10425572
The two main options are bilinear mapping and projective mapping.

A bilinear mapping is
p(u,v)=(1-v)*((1-u)*p00+u*p01)+v*((1-u)*p10+u*p11). The p?? are the vertices of the quadrilateral.
A projective mapping is
p(u,v)=[x/w,y/w] where [x,y,w] is a linear transformation of [u,v,1].

A bilinear mapping maps lines of constant u or v to straight lines, but diagonal lines become quadratic curves. A projective mapping always maps lines to lines.

For a bilinear mapping, the forward mapping is trivial, the inverse is a bit harder to calculate (quadratic formula).

For a projective mapping, calculating the transformation from the 4 points involves solving a fairly trivial system of linear equations (8 equations in 9 unknowns; the system is homogeneous, so multiplying all coefficients by the same factor leaves the result unchanged). Calculating the inverse mapping from the forward mapping is just matrix inversion.

[Anonymous No.10426187]

>>10415330
Harmonic series/overtones generrate fifths, octaves, and thirds naturally. That's why 1-3-5 and minor pentatonnics are prevalent in music.

[Anonymous No.10426261]

>>10425090
>this shit is so easy
describe your algorithm

[Anonymous No.10426620]

>>10426261
I don't look for numbers, I look for continuous structures. That is I first sorted the pieces by end pieces, corners and straights. Since there are 3 structures and 6 end pieces I knew there will be no open ends. So I attached them till I got no open ends left. Then I checked if I can get the numbers and if not I modify the structure to a slightly different one. In the end I had to modify my structure twice.

[Anonymous No.10426675]

Are you smart enough for a math degree if you find your intro to proofs course to be relatively easy and fun? (Assuming this feeling actually lasts)

[Anonymous No.10426681]

>>10419145
Thank you very much.

[Anonymous No.10426691]

How does the \cite{} command work in LaTeX?

\begin{thebibliography}{9}

\bibitem{einstein}
Albert Einstein.
\textit{Zur Elektrodynamik bewegter K{\"o}rper}. (German)
[\textit{On the electrodynamics of moving bodies}].
Annalen der Physik, 322(10):891–921, 1905.

\end{thebibliography}

I have this at the end of my document, just before \end{document} and the references page is created as it should, but whenever I try to add \cite{einstein} somewhere in the text it just shows up as einstein in bold text, not [1] as it should.

[Anonymous No.10426727]

>>10426675
It depends heavily on the school, I think. There's plenty of high level math unis that are pretty much for geniuses only and anyone who even asked himself that question won't make it.
But for a normal tier university you should be able to trust your instincts if you feel the courses are easy.

[Anonymous No.10426829]

do there exist stray protons, neutrons or electrons that aren't part of any atom?

[Anonymous No.10427047]

>>10426675
Certainly. It means you actually enjoy what math is about. You just need to add in perseverance and effort, roughly proportional to your intelligence/how fast of a learner you are.

[Anonymous No.10427116]

>>10426829
A hydrogen ion is just a proton. Nuclear fission and fusion emit free neutrons (which decay to a proton, electron and anti-neutrino). Neutron stars are presumed to consist primarily of neutrons (hence their density).

Electrons aren't even really "part of" an atom. Atomic nuclei are positively charged, so electrons will tend to orbit them; but in a solid, electrons move quite freely between atoms (and the number of electrons isn't constrained to match the number of protons; any lump of matter which has a negative static charge has some excess electrons). In a plasma, many or even most of the electrons are unbound.

[Anonymous No.10427499]

So um, can a function mapping members of an infinite set to another (infinite set) be surjective? I assume every single member of the codomain could be hit, even if it has an infinite number of members. And couldn't it also be injective as well?

[Anonymous No.10427607]

Brainlet here. I have a maths exam coming up (nothing too crazy, probably somewhere between calc 1/calc 2) and I'd feel much more comfortable in it if I could quickly generate graphs.

The rules are that it must be a non-programmable "scientific calculator", with additional restrictions in pic related. These are obviously intended to rule out anything resembling a traditional graphing calculator. But I noticed that, strictly speaking, they don't forbid the ability to simply auto-draw a graph (as long as it can't then differentiate/integrate it for me).

Are there any calculators that can render a graph for me but do not offer any calculus features? I couldn't find any with a quick look on Amazon.

[Anonymous No.10427843]

I'm almost certain I've failed Calculus II for the semester.

Is it better for me to withdraw from the course before the withdrawal penalty, or stick it through to see all the material, bomb the final, and then re-take to do grade replacement?

Either way I need to take the course over.

[Anonymous No.10428085]

>Where X is the data n is the number of samples
Is this true? Can you calculate a covariance matrix by doing this?

[Anonymous No.10428403]

>>10427843
That's a question for your academic adviser, not 4chins

[Anonymous No.10428526]

x'' = -kx

I know that the solution is
x(t) = A*sin(sqrt(k)*t) + B*cos(sqrt(k)*t)
but how do we get that? How do we actually solve the differential equation?

[Anonymous No.10428658]

>>10426620

OP here, good heuristic, I was trying something similar for days. You can do almost the entire game (and this level too) by just fucking around intelligently like this, but I just couldn't see this one. Once I'd had enough I tried bruteforcing by actually counting all conceivable 17s (to eliminate material), setting those first and then playing with the rest and I still couldn't get it.

[Anonymous No.10428696]

>>10427843
>bomb the final
Don't count on that if you're "almost certain" you've failed. You can find Calc material literally everywhere on the web; maybe even from your institution if you ask older students or somebody in the same course (who you know won't withdraw)

[Anonymous No.10428726]

>>10428696
by bomb the final, I mean fail it spectacularly so I can't accidentally pass with a low D.

[Anonymous No.10429247]

>>10428526
> How do we actually solve the differential equation?
The general-case solution for linear ODEs (and systems of linear ODEs) is the Laplace transform. L{df/dt}=s*L{f}-f(0). This can be repeated to obtain nth derivatives: L{d^2f/dt^2}=s^2*L{f}-s*f(0)-f'(0) The result is L{f}=G(s)/H(s) where G and H are polynomials. H(s) is factored and G(s)/H(s) is decomposed into partial fractions, i.e. a sum of terms with the form a/(s-k)^n where the k are the roots of H. The inverse transform yields terms of the form a*t^(n-1)*e^kt, and the solution to any system of linear ODEs consists solely of such terms. Note that if k is complex then e^kt=e^(a+ib)t=e^at*e^ibt=e^at*(cos(bt)+isin(bt)). For ODEs with real coefficients, complex roots always occur as conjugate pairs so the imaginary parts cancel and you get a real solution.

For the case of x''=-kx, you get
s^2X-sx(0)-x'(0)=-kX where X=L{x}
=> (s^2+k)X=sx(0)+x'(0)
=> X=(sx(0)+x'(0))/(s^2+k)
=> X=(sx(0)+x'(0))/(s+iw)(s-iw) where w=sqrt(k)
=> X=a/(s+iw)+b/(s-iw) where a+b=x(0), b-a=x'(0)/iw
=> x=a*e^-iwt+b*e^iwt
=> x=(a+b)cos(wt)+(b-a)isin(wt)
=> x=x(0)cos(wt)+(x'(0)/w)sin(wt)

Of course, you can just take the second derivative of x(t)=a*cos(wt)+b*sin(wt) and note that x''(t)=-w^2*x(t), but that doesn't tell you whether there's a more general solution. With a homogeneous ODE (where there is no constant term), if F(x)=0 and G(x)=0 then a*F(x)+b*G(x)=0. So the general solution is a weighted sum of all linearly-independent specific solutions.

[Anonymous No.10430015]

>>10428658
Once you have a structure with no open ends you are basically done because it gets very easy from here. The hard part is finding your first closed structure. You must be willing to make radical changes to your structure if you see you can't close it. Also, I closed the corners first with L shapes and turns out the final structure has two of those at the top left and bottom left and also somewhat on the top right. So this strategy probably helped me quickly converge towards a closed structure.

[Anonymous No.10430159]

If the earth rotates 465 m/s, how come flying objects don't immediately disappear? How do they stay in the same place?

[Anonymous No.10430175]

>>10415960
https://en.wikipedia.org/wiki/Art_gallery_problem

[Anonymous No.10431035]

>>10430015
so basically you applied the obvious strategy that probably 99% of players use and lucked upon the correct answer early

[Anonymous No.10431068]

>>10431035
the strat I used by default will lead to the correct answer within 10 minutes max

just admit you are an idiot too incompetent to use basic strategic thinking

[Anonymous No.10431070]

>>10427499
After getting some actual sleep I realized how retarded this question is. Jesus Christ.

[Anonymous No.10431133]

What are some jobs taht would suit for sociopaths? Psychology seems to be the best, but the salary and future application looks debatable almost funny.
>asking for a friend

[Anonymous No.10431289]

This is from some pdf I found about control systems after digging for quite a while.
Where I'm from the x(t) equation is known as "Lagrange's formula", but I can't find a thing about it in English. Also, the (e^At)x(0) term is called "free motion", and the other one "forced motion". Has anyone who's taken a control systems course in English ever referred to these components by those words (or something similar) or are they known by some other name? Wikipedia isn't helping; maybe I haven't come across the right article yet.

[Anonymous No.10431452]

>>10431133
fetching dead bodies for funerals

[Anonymous No.10432977]

>>10431068

Not that it matters anymore, but it was the OP, after all. That post was made by someone who is not the OP (though he does have a valid point). I, the OP, was the one who wrote the thanks so that I can put this stupid puzzle behind me, which made someone (you?) feel bad. I then also wrote this one. >>10428658

There /was/ an element of luck to your solution, (no there wasn't) yes, there was, which I can freely write now that the thread's purpose has been fulfilled, so that I can (again) put this nonsense behind me and not have an anyuresm a few weeks later. I was doing everything you were doing, for a few hours, and I will hazard to say, about as intelligently. In particular, I freely/radically changed up the "three chains" using the same observations you've described when a given approach didn't seem to be working. I came up with about 5-10 distinct "closed forms", some with one proper sum, but which failed to solve. I just plain didn't see it. It's because I understood the role of chance to a solution (the rest of the game works this way too) that I cut my time and farmed the solution out to my local cuck: you. You had a wonderful chance to TANTALIZE me by not actually providing a solution, or instead presenting a partial/misleading one, yet you didn't. You provided me exactly what I asked for. Who's retarded now? :^)

[Anonymous No.10433757]

>>10432977
Ok so you wasted countless hours trying to solve it and fail. You beg for help on an anime forum like a little bitch. I solve it in a couple minutes because I was bored and enjoy solving problems I haven't done before. And now you whine
>I-ITS JUST LUCK! Y-YOU ARE THE KEK NOT ME!
Ok, whatever makes you sleep at night. I hope you one day recover from the trauma this game has given you.

[Anonymous No.10433949]

Let's say someone is trying to prove an expression is true for all natural numbers without using induction. If the person chooses a proof by exhaustion (or an induction proof with cases I guess). Do they have to have cases that relate the sizes of the different numbers involved ? Or can they just use two cases : n is odd or n is even? I want to think the latter is okay since a natural number is either one or the other. And odd numbers are the successors of even numbers and vice versa. But it's an expression with three natural numbers so I assume you have to relate their sizes. Also is size a bad term to use when describing numbers?

[Anonymous No.10433965]

Here's a real stupid question for you

Should I add a paper as a reference in my thesis even If I do not point to it directly in any sentence?
I've read a shit ton of them and added them all as my references but my text does not really rely on all of them

[Anonymous No.10435034]

Yo nigggaz. Am back to highschool coz i never got my degree and here i am lmao.
In my biology textbook in the beginning it says "something that shows all the 7 crucial life signs" one of them being reproducing. Lmao, does this mean virgins/infertile people are not alive?
I am aware I am retarded, as I do have the life sign “observing"

[Anonymous No.10435429]

How do I know when to use polynomial long division to get 10δ?

When F(S) = 8(s^2-5s+50)/(s^2(s+10)) how come there isnt an 8δ for the inverse laplace?

[Anonymous No.10435504]

Is it possible to have a context-free grammar G in chomsky normal form such that some string in L(G) has a parse tree consisting of 6 nodes? how?

[Anonymous No.10435680]

>>10428726
ah, shit. Never heard the expression before. If you won't get any sort of penalty for failing (this includes possible postgrad grants in the future, etc.), go for it so you get to see what to expect when you retake it.

[Anonymous No.10435837]

>>10432977
>I came up with about 5-10 distinct "closed forms", some with one proper sum, but which failed to solve.
Can you show us one?

Also I notice you guys missed >>10423894 this guy posted the same solution (1 swap off) 12 hours earlier than our angry autistic anon.

[Anonymous No.10435844]

>>10422932
in literally 3 seconds I got 130/3 so try verifying your answer again

[Anonymous No.10435955]

why are ratios in solution chemistry so retarded?

a 1:10 dilution of A in B means what?
>1 parts A and 10 parts B?
WRONG
it means 1 parts A and 9 parts B.

when did this retarded convention to use ratios incorrectly start?

[Anonymous No.10435992]

>>10412555
Hey guys, no stupid questions right?

I was wondering whether resonance such as electrical could have direct effect on psychology, especially fragile minds. I wondered what frequency our consciousness resonates at.

I wonder if Schumann resonance as alleged in Lain (serial experiments) could perhaps influence a global collective consciousness (that we could allegedly enter when in a dreamlike or trancelike state).

My question centers around the origin of consciousness and extends from basic theorem of physics into quantum physics which would basically require big brain kind of knowledge and I don't expect an answer as I myself am just a highschool dropout with minimal academic experience to trade off or converse with you in any continuous sense.

What I'm asking is that if you are in the field of physics or engineering to any degree, could you begin to ask yourselves questions about how your work field impacts consciousness from a basic psychological to a greater - theory-of-numbers level.

I realise I'm babbling, I'm sorry... It's hard for me to articulate what I'm saying.

Basically my view is this;

>consciousness is not a constant
>it is influenced by resonance in frequency
>electrical circuits surrounding us every day (power lines, power cables in our homes, power circuits in our computer circuit boards)
>the binary value of 1-0 on/off can be assigned to a circuit that is complete/incomplete

>where

>some part of consciousness or influence upon consciousness

>could be quantified by

>measuring how many electrical circuits one is influenced by on average in a day

>experiments to range in the questions of

>does the rate of electricity flowing through a circuit impact consciousness and if so to what extent

>does the impact of consciousness altering through resonant frequency greatly affect the mental health of any or some subset of people (statistics)

>fuck
i realise i might as well be asking you to search for the answer to life...

[Anonymous No.10435999]

Why doesn't my method work?

[Anonymous No.10436002]

>>10435992

>here is something that i watched a while ago that may inspire you to look past my babble

If you have ever questioned the nature of your consciousness and you are specifically in the STEM fields... I urge you to watch.

https://youtu.be/pLbSlC0Pucw

[Anonymous No.10436004]

>>10435999
The problem is to find the velocities of the masses after they're released from rest.

[Anonymous No.10436033]

>>10435999
you integrated w.r.t. r and not t

[Anonymous No.10436071]

>>10436033
You're right, that was very stupid of me, however even if I had, my answer would still be wrong.

[Anonymous No.10436099]

Is there a place where I can download complex mechanical blueprints?

something like pic related for an assembly but with actually legible measurements

something to practice with and add to my drafting portolio as a mech engineer major

[Anonymous No.10436100]

>>10435429
Bump

[Anonymous No.10436145]

>>10435837

Since someone's curious, here we go again...

It's important to note (as I did, in the OP) that strictly speaking, chains do not have to be "closed", though they almost always are. All that is required is that the sums are linked up, not linking to each other, and partition correctly. In one level, (28, right) the game plays with an over-abundance of connections, and the task is to "disconnect" these just enough to satisfy yadda-yadda. Since I knew that this was true and did not see the solution, I did begin to consider the known possibility that such a "messy" solution might exist for 49. Fortunately I didn't waste too much more time on this idea, both as the spirit of the level (six end-connections) and the game's norm strongly pointed to the closed chains.

[Anonymous No.10436222]

>>10435429
Partial fraction decomposition by itself only works if the numerator is of lower degree than the denominator. In that case, polynomial division gives you a quotient of zero, with the original expression as the remainder. So you can just skip the polynomial division step.

[Anonymous No.10436277]

can someone please explain my stupid ass what does the convolution operator do? i know how to work with it and a few basic properties since i just started reading about it a few days ago, but i can't for the life of me imagine what it actually represents and why we need it other than having some operations with fourier transforms behave rather nicely

[Anonymous No.10436515]

>>10436145
>Since someone's curious, here we go again...
indeed if we take the "there's 3 chains and 6 end pieces I knew there will be no open ends" (from >>10426620) as true, there's still numerous arrangements possible.
sadly, angry anon's logic isn't true in general, it only happens to work out in this particular level because there are no pieces with 3 connections. but he didn't include that in his explanation so at that point it was clear he was a drooler who just happened to arbitrarily start his search close to the solution.
i was hoping he'd had some kind of valuable insight though. oh well.
btw, i'm the "someone who isn't OP" you referred to earlier and also wrote >>10413895

[Anonymous No.10436516]

>>10435955
it's so you can measure the total volume and not the separate volumes, which allows you to use a single volumetric flask (add A up to number 1. Add B up to number 2.)

[Anonymous No.10436528]

>>10436145
>Since someone's curious, here we go again...
indeed. even if we take the "there's 3 chains and 6 end pieces I knew there will be no open ends" (from >>10426620) as true, there's still numerous arrangements possible which must be exhaustively searched.
sadly, on top of all that, angry anon's logic isn't true in general, it only happens to work out in this particular level because there are no pieces with 3 connections. but he didn't include that in his explanation so at that point it was already clear he was a drooler who just happened to arbitrarily start his search close to the solution.
i was hoping he'd had some kind of valuable insight though. oh well.
btw, i'm the "someone who isn't OP" you referred to earlier and also wrote >>10413895

[Anonymous No.10436719]

>>10436277
Convolution performs a linear, time-invariant filter operation.
Linear: a∗(b+c)=a∗b+a∗c, a∗(kb)=k(a∗b).
Time-invariant: if f2(t)=f1(t-T), g1=a∗f1, g2=a∗f2 => g2(t)=g1(t-T).

The Dirac delta function (impulse) is an identity for convolution, i.e. f∗δ=δ∗f=f. So if you treat a signal as a sum of scaled, time-shifted impulses, convolving the signal with a given function gives you the sum of scaled, time-shifted copies of that function.

A rolling average is a discrete convolution, where the weights are always positive and sum to unity.

Several basic image-processing operations (blur, sharpen, edge detection) are convolution operations.

[Anonymous No.10436724]

Intro to point-set topology/undergrad topology. This course is kicking my ass, please help.

[Anonymous No.10436725]

>>10436724
This one too please <3

[Anonymous No.10436729]

>>10412555
May someone help me on these two questions?

[Anonymous No.10436732]

>>10436729
>>10436725
>>10436724
What have you tried?

[Anonymous No.10436742]

>>10436732
For the first part of question 24:
a≡b(mod5)
a-b=5k
x≡y(mod5)
x-y=5l
k,l,m=integers

a+x≡b+y(mod5)
(a+x)-(b+y)=5m
(a-b)+(x-y) =5m
5k + 5l=5m
5(k+l)=5m
k+l=m
And for the second part, I couldn't complete it:
ax≡by(mod5)
ax-by= 5q
q=integer
–5k/b*(-5l/y)-by=5q
25kl/by-by= 5q
25kl-b2y2=5qby
I'm sorry that I can't use TeX.

[Anonymous No.10436750]

>>10436528
>>10436145
lol youre so butthurt
>he didn't include that in his explanation
because thats obvious

>pic related
hey its my "second form"

let me show you how I got to the solution step by step so even you low intelligence idiots might understand it. give me a moment to reconstruct that shit

[Anonymous No.10436752]

>>10436742
Your first solution is correct, assuming you define m to be k + l. In the second part, it looks like you've made the wrong assumption that a = -5k/b. It's not. a - b = 5k, so a = b + 5k. And similarly for x.

A correct solution would go like this: rewrite a as b + 5k and x as y + 5l so that ax = by + 5ky + 5lb + 25kl and hence ax - by = 5q, where q = ky + lb + 5kl. Hence, ax = by mod 5.

Question 25 is the same except you replace 5 by d.

[Anonymous No.10436756]

>>10436750
here first I got the one on the left

obviously didnt work so I did some changes and got the middle one. didnt work again obviously so I moved only 2 pieces and voila you have the solution in front of you

[Anonymous No.10436762]

>>10436752
Thank you.

[Anonymous No.10436769]

>>10436762
You're welcome.

[Anonymous No.10437058]

Can i do a chi square test on non gaussian data?

[Anonymous No.10437227]

I feel particularly retarded for asking this question, doubly so because I am math retarded, but this is for my intro astronomy extra credit my teacher passed out. I'm less looking for the answer and more looking for a better understanding so I can solve this shit on my own in the future.

"Hypothetical planet has the same mass as Earth, but is twelve times smaller. What would the gravity be like on this hypothetical planet as compared to Earth's?"

It's a multiple choice sort of question. 12 times weaker/stronger or 144 times weaker/stronger. I'm 100% sure it gets stronger, but my math is toddler tier so I'm not sure if it is just 12 times stronger or if you're supposed to square it by 2.

[Anonymous No.10437246]

>>10437227

The formula for gravitation field strength (acceleration due to gravity) is given by[eqn]g=\frac{GM}{r^2}[/eqn]where G is Newton's constant of gravitation, r is the distance from the mass, and M is the actual mass.

Since [math]M[/math] and [math]G[/math] are constant, and [math]g\propto{\frac{1}{r^2}}[/math], it can be seen that 12th-ing the radius would increase the field strength by 144 times.

[Anonymous No.10437266]

>>10437227
Think of it as a function of the distance, [math]g(x)=-\frac{GmM}{x^2}[/math]. If the Earth's radius is [math]r_e[/math], then [math]g(r_e)[/math] is the gravitational pull perceived by an object on mass [math]m[/math] on Earth. If your hypothetical planet's radius is 12 times smaller than Earth, simply evaluate [math]g(r_e/12)=-\frac{GmM}{(r_e/12)^2}=-\frac{12^2GmM}{r_e^2}[/math].

[Anonymous No.10437293]

>>10437246
>>10437266
Alright, I think I'm slowly starting to understand the method now. As someone new to scientific notation, and being uneducated is most math, I'm still trying to wrap my head around some of the reasons of "but why"? For example, why does r(adius?) become squared by 2? Likewise, what does the small e stand for in the second explanation?

[Anonymous No.10437308]

>>10437293
Nothing important — in physics it's common to name variables that way. Say, if I'm solving a problem that involves the mass and volumes of three objects A, B and C, I might write the masses as [math]m_A,m_B,m_C[/math] and the volumes as [math]v_A,v_B,v_C[/math] to remind myself (and the reader) of what these variables mean.

Of course, there are mathematical operations and symbols that use the subscript to denote an actual variable or quantity; e.g. a directional derivative [math]D_zf(x)[/math], or the first few terms of the Fibonacci sequence [math]F_1=1,F_2=1,F_3=2,F_4=3,F_5=5...[/math]. Usually, the meaning is clear from context so don't worry too much about it.

[Anonymous No.10437321]

>>10436277
intuitively, convolution is mapping the change in the shared area between two functions, as one passes over the other.

[Anonymous No.10437323]

>>10437321
another neato graph

convolution has got to be my favorite operator, it absolutely blew my mind when I first learned about it

[Anonymous No.10437342]

>>10437308
I feel slightly less dumb than I did before, so I definitely appreciate the help. Thanks!

[Anonymous No.10437483]

Hi /sqt/,
I'm currently learning for a test on numerical maths. in many approximations there is
[math] f'(x) \approx f(t,y)[/math]

I can't wrap my head around this as i imagine f'(x) as a slope and f(t,y) as a point. could you direct me to a place where i can read up about this or give me a brainlet explanation pls?

[Anonymous No.10437490]

see this (+sub) and uor brain is long cyкaблятьhttps://www.youtube.com/watch?v=NmJKOda40Y4

[Anonymous No.10437660]

how the H*CK do I get good at proving trig identities?

[Anonymous No.10437752]

>>10437660
Do them once and remember how you did it.

[Anonymous No.10437844]

I'm solving a characteristic polynomial with some some initial conditions and this is the solution.
Why is theta = -pi/2?
Why can't I just use pi/2 and let c= -2?

[Anonymous No.10437848]

>>10437844

[Anonymous No.10437913]

>>10415330
ALWAYS

[Anonymous No.10437971]

>>10437844
That would also work, yes. You could also have theta = pi/2 + n*pi for any whole number n and this would satisfy the two initial condition equations you posted.
I assume you're going to plug theta and c into the solution of some differential equation right? Does the solution change at all if you have different values of theta and c that satisfy the initial conditions?

[Anonymous No.10438020]

>>10437971
Nah, they don't change.

[Anonymous No.10438023]

>>10438020
As expected.

[Anonymous No.10438046]

can someone explain how to solve this?

I know I must distribute the parenthesis, however this nigger online test gives me wrong this question.

[Anonymous No.10438063]

>>10412555
Current through a 300mH coil increases at a rate of 50uA per 10us, how much is the induced voltage?

I think it should just be V=L (di/dt), which I computed as 1.5V but the correct answer is 1.5kV

[Anonymous No.10438091]

>>10438063
Looks like the "correct" answer is wrong and you're right.

[Anonymous No.10438096]

>>10438046
-2t-(-3(2t-r)+6(t-3r)) = -2t+(-1)(-3(2t-r)+6(t-3r))

[Anonymous No.10438117]

>>10438091
Thanks, just wanted to get a second opinion before I emailed the instructor and made an idiot of myself since someone did score 100% (meaning they came up with the 1.5kV value). It's the only problem I missed.

[Anonymous No.10438434]

Could someone point me in the direction of a solution manual for this?

[Anonymous No.10438449]

>>10438046
-2t-(-3*2t)+6t -(-3*(-r))+6*(-3r)
-2t+6t+6t-3r-18r
10t-21r
you could also first observe -(-3(2t-r))=3(2t-r)

[Anonymous No.10438454]

>>10437660
unit circle helps a lot for the angle difference identities, which give you all the other ones
a lot of the time the purely algebraic proof is the least useful for intuition
in general, once you learn a proof, try to write it down from memory without using your book

[Anonymous No.10439179]

>>10437660
The basic ones all come from the definitions of sin/cos/tan/sec/csc/cot, Pythagoras' theorem, and elementary algebra.

The sum/difference identities can be derived easily enough from a diagram, but it's probably simpler to note that if R(a) is the 2x2 matrix
[cos(a) -sin(a)]
[sin(a) cos(a)]
corresponding to a rotation of angle a, then R(a+b)=R(a).R(b).

The multiple angle formulae are just the sum formulae with repeated arguments, sin(2a)=sin(a+a), sin(3a)=sin(2a+a), etc. Fractional angle formulae are just the inverse, i.e. solving a quadratic/cubic/etc polynomial in sin(x/n) or cos(x/n) (but it starts getting a bit awkward because you have multiple roots and have to choose the correct one; sin^2+cos^2=1 => sin=sqrt(1-cos^2) OR sin=-sqrt(1-cos^2); for any given angle, only one of those is correct).

[Anonymous No.10439202]

>>10425376
I am at an R1 uni in the Midwest/Big10, not ranked that high, but should be known. Doing electrical engineering, courses are specializing in lasers and optics and want to do shit in that area for grad school as well. GPA is 3.8/4.0, all As in relevant coursework, havent taken GRE but will soon, it doesnt seem that difficult. Worried about letters of recommendation if I dont do research as they would all just be from inclass relationship which wouldnt be as thorough. For schools I was looking at URochester (has a whole department for optics etc, heard it was the best program), CUBoulder, UWashington, and then maybe some like minnesota, wisconsin, with my current university as a safety school.
Quick rundown on JUST how fucked i am?

[Anonymous No.10439249]

>>10436528

I'm the OP. Don't sympathize with me too much. My cuck got the solution, and neither of us did. :^)

[Anonymous No.10439330]

I remember reading an article about p-hacking and replication crisis and there was a quote from some famous scientist about how he doesn't trust any studies published in the last 50 years or something like that, does anyone know what could that quote be or any famous scientists critical of the modern science? I've tried to find it but it's been more than ten years since google became useless for vague searches like that.

[Anonymous No.10439902]

There are two urns, one of which contains 5 white and 3 black balls and the other one contains 2 white and 4 black balls. Two balls are taken from the each urn. X represents the number of white balls taken from the urns. Find the mean of X.

[Anonymous No.10439931]

>>10439202
check this thread out: >>/sci/thread/S10248549#p10248549

[Anonymous No.10439934]

>>10439902
I think for urn 1, probability of the first ball being white is 5/8, and the probability of the second being white is (5/8)*(4/7)+(3/8)*(2/7).
Can you try urn 2?

[Anonymous No.10440048]

If I generate 1 million random numbers in one set in the range 1 to 1 million, then generate 10,000 more in the same range in a new set, is it more or less guaranteed that around 1% will match?

[Anonymous No.10440082]

>>10439931
that actually helps a bit, thanks

[Anonymous No.10440095]

In Java how do I do something 1% of the time?

[Anonymous No.10440097]

>>10412555
How 2 get smart

[Anonymous No.10440157]

>>10440048
Out of 10,000 random numbers, you'd expect to get ~9950 distinct numbers (with the other 50 being duplicates). So you'd expect ~0.995% of the million numbers to occur in the smaller set. Also, you'd only expect ~632,000 distinct numbers out of a million, with ~368,000 being duplicates.

[Anonymous No.10440390]

>>10440157
Thanks

[Anonymous No.10440404]

Shouldn't a rocket's Max Q always be the sound barrier ? On every launch I've watched it's always a bit before or after going supersonic.

[Anonymous No.10440494]

This seems like the best board for this but:
How do some crimes remain unsolved today? Isn't there always a plethora of DNA evidence to be found at any crime scene? Is it just laziness on the part of the investigators or what? It seems like with fingerprints, hair, and all that forensics ability, finding a criminal would be a cinch.

[Anonymous No.10440523]

>>10440494
they need a reference dna sample still, if the criminals dna isnt in the system it wouldnt match

[Anonymous No.10440534]

>>10440523
Yeah, but like, most kids did the thing where the cops take your fingerprints in school, don't they? You'd have to be planning from 5 years old to make sure you don't give your fingerprints.

[Anonymous No.10440539]

>>10440534
>Yeah, but like, most kids did the thing where the cops take your fingerprints in school, don't they?

Do americans really do this?

[Anonymous No.10440542]

>>10440539
Yes.

[Anonymous No.10440551]

a^b=c

What is a value of b that would make c be less than zero assuming a is positive?

[Anonymous No.10440604]

>>10440523
Yeah, but then all they would have to do is find the suspects, which is pretty fucking easy, since they have access to cameras, your phone records, your online posts, everything.

[Anonymous No.10440632]

>>10440551
[math]i \pi [/math]

[Anonymous No.10440642]

>>10440632
Or [math] i \pi \ln a+x [/math] for any real x if you want to be the most general

[Anonymous No.10440739]

I am looking for a simple and preferably cleaner, less clunky solution to this rather simple system of equations (see pic related).

While I did find the correct answers, the way I solved it seems absolutely braindead because arriving to the answers took me quite some time even though the problem is supposedly an incredibly easy one.

For more information: G is known, S1 and S2 is what I'm looking for.

If anyone knows a better method, it would be incredibly appreciated.

[Anonymous No.10440919]

Help with a baby tier analysis proof?

Basically, for a sequence bounded in an interval in the reals, then that sequence with an added factor of 1/n will converge to a real number.

So far I've tried to show that, since our arbitrary given sequence is bounded above and below, the limsup and liminf of that sequence are also within the interval. My hope is to show that the subsequences that approach the limsup and liminf, when having the added factor of 1/n, will clearly approach a specific real number, ie that the limsup=liminf But I'm a little lost and I don't know if this is a good approach.

[Anonymous No.10440920]

>>10412555
Hi, I need help with some linear algebra stuff. How do you prove this? I'm not sure I'm understanding what the triple equal is supposed to mean here and how to approach it.

[Anonymous No.10440938]

>>10440920
Triple equals sign means "defined to be," ie that ordered pair you've got there is defined to be a vector in two dimensional real space where either 1 component is 0 or the other is 0.

It's just like saying equals, kinda. Triple equal sign is more common in physics so it's odd your linear algebra professor would use it, typically in maths people use ":="

But it's all just notation. Triple equals sign can also mean "is congruent to" in number theory

[Anonymous No.10441000]

>>10440938
Thanks, I think I figured it out.

[Anonymous No.10441012]

>>10440919
I think you could directly show that the new sequence converges to zero.
Show that for every epsilon>0 there exists corresponding N such that when n>N, we have abs(s_n / n) < epsilon. You'll need to use the fact the original sequence (s_n) is bounded.

[Anonymous No.10441113]

>>10440534
nigga what? i could see them taking dna when your born or giving blood, but you took some class where you got fingerprinted?

[Anonymous No.10441119]

>>10441113
They structure it like a field trip. They do it really young too so the kid doesn't have enough brain capacity to think "hey maybe I might need to rebel against the state at some point." They give parents a document saying "hey we're going to fingerprint your kids and put them in a national database."

[Anonymous No.10441183]

>>10441119
i never did that in my life, do you live in the south or a big city?

[Anonymous No.10441185]

>>10441183
Arizona, Phoenix.

[Anonymous No.10441189]

>>10440739
Why don't you treat it as an equation in [math]\mathbb{R}^2[/math] and simply invert the matrix?

[math]G + \begin{bmatrix}\cos \alpha & \cos \beta \\ \sin \alpha & \sin \beta \end{bmatrix} \begin{bmatrix} S_1 \\ S_2 \end{bmatrix} = 0[/math]

For a 2x2 matrix, the inverse is really easily written down:
[math]\begin{bmatrix}\cos \alpha & \cos \beta \\ \sin \alpha & \sin \beta \end{bmatrix}^{-1} = {1 \over \cos \alpha \sin \beta - \sin \alpha \cos \beta} \begin{bmatrix}\sin \beta & -\cos \beta \\ -\sin \alpha & \cos \alpha\end{bmatrix}[/math],
and that determinant in the denominator is of course [math]\sin(\beta-\alpha)[/math]

I don't know whether you perceive that as easier or simpler, let us now..

[Anonymous No.10441378]

What do you call this black square glass thing?

[Anonymous No.10441397]

>>10441378
a table?

[Anonymous No.10441409]

>>10441397
No, it's the thing you put between the bunsen burner and the flask, like a glass or ceramic slide to act as a heat buffer.

It looks bigger in the image I posted but it's actually just 5 inches or so on the side.

[Anonymous No.10441438]

I'm genuinely retarded. Generally, how would I begin solving the total resistance of something like this?

[Anonymous No.10441565]

Shouldn't this be the intersection of L2 and 0*1*??

[Anonymous No.10441628]

currently doing some calc 2 practice
when using newtons law of cooling, do the temperature values have to be in C or K? I've never gotten an example in Fahrenheit until now and I'm not entirely sure if I should change it or anything
I'm assuming I should

[Anonymous No.10441631]

>>10441628
Leave it in Fahrenheit because it's a math question. If it was a science question, you should convert it to Kelvin.

[Anonymous No.10441636]

>>10441628
Do they bunch in DE in your Calc2 course?

[Anonymous No.10441641]

>>10441636
yes
>>10441631
but wouldnt this affect calculations since the differences between fahrenheit values and K/C are different?

[Anonymous No.10441643]

>>10441628
the heat transfer coefficient has inverse units of temperature. So if it's in F you need a different constant or to convert. But the temperature scale does not need to be absolute because the law takes temperature DIFFERENCE as an input

[Anonymous No.10441649]

>>10441438
Kirchoff's laws?

[Anonymous No.10441653]

>>10441649
That's not for effective resistance. I found out I could use Wye-Delta conversion just now so it's good now

[Anonymous No.10441663]

>>10441409
I dunn. Heat spreader? I think most people would call it a ceramic plate and be done with it.

[Anonymous No.10441668]

>>10441653
Kirchoff's laws can indeed be used to derive effective resistance in such cases, this is a common intro physics problem.

http://softschools.com/notes/ap_physics/kirchhoffs_rules_and_resistors_in_series_and_parallel/

[Anonymous No.10441742]

can someone explain what the fuck happened here?

[Anonymous No.10441758]

Why wouldn't you just click the question mark?

[Anonymous No.10441770]

wow why didnt i think of that

[Anonymous No.10441778]

>>10441742
Double angle identity + [math]\cos a = \sqrt{1-\sin^2 a}[/math]

[Anonymous No.10441802]

>>10441778
im not picking up what you're putting down in the slightest
how is cosine involved in sin(2arcsin(a))?

[Anonymous No.10441831]

>>10441742

I/m gessin that someone substituted that arcsin shit for u to make the integral easier to solve, then plugged it back in after they were done.. no?

isn't arcsin the angle.. so a number? isn't all that multiplied by x just a constant? that's probably why they took it out in the first place.... now I guess they just put it back in right?

[Anonymous No.10441847]

>>10433757
look Im sorry

[Anonymous No.10441850]

>>10441831
youre losing me doc

[Anonymous No.10441933]

>>10440523
Suspects have been tracked from genetic profiles of relatives uploaded to ancestry sites like 23andme. But unless the quantity and nature of the crime-scene DNA is such that it's reasonably certain to have come from the criminal, DNA only gives you a lead. Trace quantities of DNA could have come from almost anywhere: someone who used the same taxi as the culprit (or the victim), sat next to them on a bus, etc.

[Anonymous No.10441947]

>>10441742
u=arcsin(x/9) => sin(u)=x/9
sin(2u) = 2sin(u)cos(u) # double-angle formula
= 2sin(u)sqrt(1-sin^2(u)) # sin^2+cos^2=1
= 2(x/9)sqrt(1-(x/9)^2) # substitute sin(u)=x/9
= 2(x/9)sqrt(1-x^2/81)
= (2x sqrt(1-x^2/81))/9

[Anonymous No.10441968]

>>10441947
thank you holy shit
i dont know whats wrong with my brain
thanks to everyone else as well

[Anonymous No.10442001]

>>10441668
That part's obvious but you're not getting what my original question intended. Thank you for the consideration though

[Anonymous No.10442005]

>>10441438
Kirchhoff's laws would work. However, the potential difference between nodes 6 and 4 is guaranteed to be zero (both are the mean of nodes 3 and 5), so you can replace R7 with a short. Thereafter, you can just use series/parallel combinations until you're down to a single resistor (2.9375k).

[Anonymous No.10442006]

>>10441409
Is it mesh? If so, it's called a mesh.

[Anonymous No.10442020]

>>10441802
anon, i...

[Anonymous No.10442105]

this may not be the best place to ask, but would getting a masters in europe fuck up any opportunities here in the US? going to grad school next year with my bachelors from the US and can go to some masters programs in europe in case i dont get into a phd in the US some how, as the euro masters degree will be cheaper and still be at a good university in the top 10 of europe for my field. Would this make it harder for industry, national lab, or maybe security clearance jobs back in the US because i was out of the country? I assume it wont hurt my chances much for going back to the US for a PhD if I want to do that afterwards

[Anonymous No.10442282]

>>10442005
That's incorrect. It would be true if node 7 was an unloaded output, but there's current drawn. KCL gives the resistance as 49/16=3.0625k.

Application of KCL

[Anonymous No.10442299]

Is this bug sex?

[Anonymous No.10442434]

>>10442299
yes

[Anonymous No.10442615]

>>10441189
Hmm, I haven't treated it that way because I haven't really seen this applied like that in a practical scenario, so thanks a lot for showing me.

Though, I have a question. The denominator, if I'm not mistaken, should be sin([math]\alpha - \beta[/math]), no?

It would mean that I'd have to take the opposite of the denominator of the determinant, I think. In either case, if this works, it's absolute genius, and I really want to thank you for it.

[Anonymous No.10442627]

>>10442615
>The denominator, if I'm not mistaken, should be sin(α−β), no?
No, the inverse is correct. You may be confused by my omitting the system it solves, namely: G + A*s = 0; in other words As = -G (note the negative), so s = A^(-1)*(-G).

>It would mean that I'd have to take the opposite of the denominator of the determinant, I think. In either case, if this works, it's absolute genius, and I really want to thank you for it.

The general form for the inverse of a matrix A is: [math] {1 \over |A| } \cdot A_{\text{Adj}}^{\text T}[/math], maybe look that if you're interested. For a 2x2 matrix:
[math] \begin{bmatrix} a & b \\ c & d \end{bmatrix}^{-1} = {1 \over ac-bd}\begin{bmatrix} d & -b \\ -c & a\end{bmatrix}[/math]

[Anonymous No.10442643]

>>10442627
Alright, thank you. This explains a lot! It seems like a much more elegant way to find the solution.

[Anonymous No.10442649]

>>10442615
>>10442627
Of course I now made a typo in there, as I'm sure you noticed: it's supposed to say ad-bc. Also, keep in mind that I used G to mean the vector (G G) in the matrix equation.

[Anonymous No.10442662]

how does vbc differ from vb?

am i right in saying

vab = 2
vbc = 1
vc = 3?

idk what vb would be then.

[Anonymous No.10442665]

>>10442662
oh wait, is Vb both of them, so v = 4?

[Anonymous No.10442706]

>>10442665
yes

[Anonymous No.10442712]

>diff eq course
>only grades are homework and exams
>we will only have 3 sets of homework all semester, and three or four exams
>each exam is 6-7 questions, 2-3 very hard, all equally weighted
>feel like I'm doomed to fail
Have you guys had courses like this? How do you survive? I'm not good at math.

[Anonymous No.10442746]

>>10442712
>more exams than hw
What the actual fuck?

[Anonymous No.10442776]

>>10442712
>How do you survive?
You practice the fuck out of it, starting right now. Do it under exam conditions. Train the way you fight, and it will work out.

[Anonymous No.10442808]

>>10442746
Technically, it's four sets of homework problems due on each date, but since we have unlimited attempts, it's not a worrying part of the grade because it's a guaranteed pass. The scary part is having 2 out of 7 questions on the exam being things we never did in class or saw explained in the book, so essentially you just hedge your bets on not getting many mistakes on the other problems and pray you pass. Combine that with low partial credit and no curve, and it's brutal. I will admit though that while I failed the first test, most people passed, but I expect the results from the second test to be much worse. Either way, it's rough.
>>10442776
You are right. I think I'm just going about this stuff wrong too. In class, I work hard to get down all the problems but rarely ever use them in studying, and I'm always tempted to just put the pencil down some day and focus instead of copying, but the idea of losing that day's notes still frightens me. The thing is, I can't both copy and learn at the same time - he just moves too fast. If I do survive this latest exam, I will have to make studying a habit and revise my learning strategies more than a little.

It really stunned me to end up with a class like this, but I suppose I no longer have ignorance as an excuse for why I'm failing, so the only option is to overcome it.

[Anonymous No.10443205]

How do i sleep less? I’ve been sleeping more and more recently. I get like 9-10 hours of sleep each night which seems kind of excessive.

[Anonymous No.10443287]

>>10442105
anyone able to help a retard out

[Anonymous No.10443350]

>>10443287
I would’ve, but I think all frogposters are fat retarded neckbeards. I hate you all.

[Anonymous No.10443373]

>>10443205
Drink coffee all day, especially in the evening. Guaranteed insomnia.

[Anonymous No.10443389]

>>10442001
>intro physics problem.
as far as i know the wye-delta conversion was derived separately by leveraging superposition of voltage sources on each node.
so please explain how to use KCL/KVL alone to solve for total resistance in this introductory problem.

[Anonymous No.10443412]

>>10443350
that is a crocodile

[Anonymous No.10443421]

>>10442808
>The scary part is having 2 out of 7 questions on the exam being things we never did in class or saw explained in the book
generally they're the same kind of problems, just presented in a different form to test you.

[Anonymous No.10443423]

>>10443389
i meant to reply to >>10441668

[Anonymous No.10443466]

How is the experience of studying in big universities like MIT?
I live in a third world country and I will never have this opportunity

[Anonymous No.10443483]

What are the best universities in Europe if I want to pursue a Masters or PhD specializing in Optics/photonics/lasers etc?

[Anonymous No.10443703]

>>10443466
my friend from high school goes there for nuclear engineering, she says classes are small and there are a lot of teaching assistants so basically everyone gets help whenever they want it. Also I guess she said her first quarter or two there is ungraded and are just counted as pass/no pass, so you dont have to get a good grade, but just enough to pass. Seems like if you get in and put in a little effort then you are set for life. She has had multiple internships with the US department of energy and will probably be making big money soon

[Anonymous No.10443779]

My father is in the hospital and may be passing away soon.
I can't afford to miss any classes. If he dies, the funeral will be held in Maryland but I live in Florida.

How do I navigate this minefield

[Anonymous No.10443840]

>>10443703
>Also I guess she said her first quarter or two there is ungraded and are just counted as pass/no pass, so you dont have to get a good grade, but just enough to pass.
This was done to curb the suicide rate from kiddos who got there from high school with perfect grades and then couldn't handle getting a B

[Anonymous No.10444095]

My network analysis class has online quizzes.
I formated my inverse laplace as Ae^bt + Ce^dt for an answer, but it shouldn’ve been Ce^dt + Ae^bt.
Literally the same answer except flipped around, yet I still lose points and my professor won’t give me anything back.
Meanwhile, this fucking indian in the same class cheated on it. We’re sittin in our other class and he blatantly copies the answer from someone else. Should I report him? Fuck this guy. Litrally not fair how he gets 100% for copying, yet I lose points for having the correct answer just formatted differently.

[Anonymous No.10444187]

CS GANG REPRESENT

How are the two functions asymptotically related?

g1 = n^3 lg(n)
g2 = n^(3.5) / lg(n)

Intuition says g1 is O(g2) by the larger polynomial coefficient. You can clearly see that g2 / g1 = sqrt(n) / (lg(n))^2. How the heck can you simplify that further? Or do you think we're just supposed to call it a day and say sqrt grows faster than lg squared

[Anonymous No.10444232]

>>10444187
>CS GANG REPRESENT
yeah there goes your help from me, queermo.

[Anonymous No.10444260]

>>10444232
thanks

[Anonymous No.10444278]

>>10444095
>online quiz
>not letting Wolfram Alpha do everything for you
lmao get a load of this guy

[Anonymous No.10444364]

>>10444278
It was literally the right answer. Fucking commutative property, a+b = b+a, yet he refuses to give back points.

[Anonymous No.10444609]

I'm first year math undergrad and I want to ask you about some interesting but not that well know topic I can "write paper" on. It could be any math or its application.

[Anonymous No.10444648]

How should I go about relearning basic mathematics (with a goal of reaching highschool aptitude)? I never commit any of it to memory. I figure I'm at a preschool level, if you hit me with 7 - 3 I have to mentally count down 6, 5, 4, rather than just having it memorized like a normal person.

[Anonymous No.10444736]

>>10444187
>CS GANG REPRESENT
kys

you could go further and prove that
[eqn]\lim_{n\to\infty} \frac{\sqrt{n}}{\lg^2n} \geq 1[/eqn]
then g2 grows faster than g1
use lhopital, simplify, use lhopital again, showing g2/g1 goes to infinity.
but if you want to really REPRESENT CS then just handwave it away and call it a day, you'll probably get full credit

[Anonymous No.10444741]

>>10444736
there are no reals in CS so using calculus techniques doesn't really make sense
...i think

[Anonymous No.10444754]

>>10444741
you don't think the concept of a limit exists?

[Anonymous No.10444765]

>>10444754
not the derivative because there's no infintesimals
there's no riemann integration

[Anonymous No.10444798]

>>10443389
> so please explain how to use KCL/KVL alone to solve for total resistance in this introductory problem.
KCL is sufficient. As all resistances are 1kΩ, I'll use units of V, mA and kΩ and just omit the resistances.

Net inbound current at each interior node:
1: v8-v1 + v2-v1 + v5-v1 = 0
2: v1-v2 + v3-v2 = 0
3: v2-v3 + v4-v3 + v6-v3 = 0
4: v3-v4 + v5-v4 + v6-v4 + v7-v4 = 0
5: v1-v5 + v4-v5 + v6-v5 = 0
6: v3-v6 + v4-v6 + v5-v6 = 0
=>
1: v2 + v5 + v8 - 3v1 = 0
2: v1 + v3 - 2v2 = 0
3: v2 + v4 + v6 - 3v3 = 0
4: v3 + v5 + v6 + v7 - 4v4 = 0
5: v1 + v4 + v6 - 3v5 = 0
6: v3 + v4 + v5 - 3v6 = 0
Current at terminal nodes:
7: v4-v7 - I = 0
8: v1-v8 + I = 0
Voltages:
9: v8-v7 = V
10: v7 = 0

10 equations, of which one (of the first 8) is redundant, in 10 variables. Treat either V or I as known and solve for the other one. V/I=49/16 is the total resistance (in kΩ).

[Anonymous No.10444801]

>>10444741
Literally shut up retard

[Anonymous No.10445089]

This is from an online quiz:

Consider the '3' in each statement. Is it a defined number (perfectly known) or does it have uncertainty associated with it (because it is a measurement)?

A triangle has 3 sides

3 mL of water was measured

3 lots of 50 mL were measured

3 scientists all measured 2.5 mL

I have to assign correct options for each statement which are:
>Defined Number so perfectly known
>Has uncertainty because its a measurement
>It is both defined and has uncertainty
>You can't tell


What the fuck is this shit?!

[Anonymous No.10445125]

Can someone please source me to a link with all of the discoveries of Johannes Kepler

[Anonymous No.10445144]

>>10416147
Your comp sci program didn't require diff EQ or probability?

[Anonymous No.10445146]

>>10418153
True that fampai.

[Anonymous No.10445322]

I am trying to understand Minkowski sum. In the pic left most square is object A and the square among green squares is object B.
Minkowski says “sweep” object A’s center about all vertices of B. For simplicity we sweep about only the boundary vertices.
The green box sweep is the A’s center sweept about all boundary vertices of B.
The black box sweep is sweept by keeping object A on the edge of object B.

Basic thing to do is to extend all x component of all vertices of object B by x component of all vertices of object A. To go to the farthest extend in x direction we have to pick farthest x in object B and farthest x in object A and add them. Is my understanding of this basic thing correct?
If yes then black box sweep seems right.
why is black box sweep wrong if it is wrong.

[Anonymous No.10445338]

Will I notice anything from 5mg of methylphenidate? I don't want to be stimmed out I just want to focus.

[Anonymous No.10445611]

>>10445338
Okay I think its just making me angry. Cool.

[Anonymous No.10445624]

Why is there need for a proof that there are infinitely many prime numbers? Shouldn't it be obvious that in an infinite amount of numbers there would be an infinite amount of both primes and composites?

[Anonymous No.10445653]

>>10435955
>a 1:10 dilution of A in B means what?
That 1/10 of the solution is made of A, OBVIOUSLY.
1:10 = 1/10.

[Anonymous No.10445667]

>>10445624
>Shouldn't it be obvious that in an infinite amount of numbers there would be an infinite amount of both primes and composites?
Pick the subset of even numbers, you still have an infinite amount of numbers yet a finite amount of primes (only 1). Sure, you might say I'm cherrypicking a specific subset to say it's not possible, but if just having infinitely many elements clearly isn't enough then why should we assume the same for all the naturals?

[Anonymous No.10445689]

By Ohm's law, could you say the voltage across a capacitor is i*z where z is the impedance of capacitor?
Or is it supposed to be 1/c * the integral of Idt?

[Anonymous No.10445713]

>>10444741
Holy shit you're retarded.
Also, just remember that log n grows slower than any positive power of n.

[Anonymous No.10445740]

How big is TREE(3)? I understand Graham's number is a bunch of threes in a power tower but the tree game is weird

[Anonymous No.10445826]

>>10445338
Next question. Is there anyway to potentiate this super low dose? God I want to kill my psychiatrist.

[Anonymous No.10445909]

>>10445689
In the time domain:
v(t)=(1/C)*integral i(t) dt.
In the Laplace domain:
V(s)=(1/s)*(1/C)*I(s)=(1/sC)*I(s)
In the frequency (Fourier) domain (which is just the Laplace domain with s=jω):
V(ω)=(1/jωC)*I(ω)=-j/ωC*I(ω)=Z(ω)*I(ω) where Z(ω)=-j/ωC

The Laplace and Fourier transforms are linear, which means that you can analyse linear networks (R, L, C, plus linearly-dependent voltage and current sources) as if they were resistor networks with complex impedances.

Moreover, they're convolution transforms, so you can describe a 4-terminal network (input pair, output pair) by a transfer function H(s)=Vout(s)/Vin(s) (likewise for ω), and the concatenation of such networks as the product of their transfer functions: H(s)=H1(s)*H2(s)*.... Whereas in the time domain you'd need to use convolution.

[Anonymous No.10445953]

>>10412555
What concepts should I understand before I get into calculus?

[Anonymous No.10445968]

>>10445953
Basic arithmetic. Calculus 1 is literally plug and chug.

[Anonymous No.10445978]

>>10412555
Hey guys, there's a graph I found in an engineering standard which I'd like to convert into variable data in table form, so it can be used for excel calculations. All numbers and letters on this picture are highlightable, but I don't know if it's possible to convert them into excel data.

[Anonymous No.10445998]

>>10445978
How mich effort do you want to put into it? If you want 100% of the information in that graph, you can extract the curves and convert the curves into coordinates pixel by pixel.

[Anonymous No.10446009]

>>10445998
I'd possibly like to do it like that. Do I use a tool for that method?

[Anonymous No.10446020]

>>10446009
>tool
Yeah you wouldn't want to do that manually of course. I don't know of any off-the-shelf program, but they probably exist somewhere. It wouldn't be too hard to write one yourself.
Another idea is that, depending on the file format of the text you got that image from, the information is already in there. Is it a PDF or postscript file?

[Anonymous No.10446030]

>>10446020
it's a pdf

[Anonymous No.10446039]

>>10446030
Maybe try this? https://automeris.io/WebPlotDigitizer/

[Anonymous No.10446058]

Brainlet here taking a basic calculus course. I understand how to use the chain rule and I thought I understood the notation for function composition, but this expression on Wikipedia confused me:

[math](f \circ g)\prime = (f\prime \circ g) \cdot g\prime[/math]

https://en.wikipedia.org/wiki/Chain_rule

Why is [math]f\prime \circ g[/math] used here to mean [math]f\prime (g(x))[/math]? I mean I can kind of see that it technically makes sense, but is it really normal to write "the derivative of f with respect to [something]" as [math]f\prime \circ \text{[something]}[/math]? Doesn't it risk confusion with "evaluate [something] and feed that result to [math]\frac{df}{dx}[/math]"?

[Anonymous No.10446078]

In linear algebra, why woulf I use LU factorization to solve a problem Ax = b (A being a matrix, x and b being vectors) when I could just row reduce A and solve for x? Basically, you could take L or U, both just row reduced A, and solve the system normally, or you could do twice the fucking work solving for Ly = b and then Ux = y (y being a vector). My teacher never answered this, she just said we have to know how to do it for the exam and moved on. I know it exists for a reason but even google wont tell me in what fucking case LU factorization is faster.

[Anonymous No.10446081]

>>10446030
>>10446039
Yeah I just tried that myself. Neat tool, I bookmarked it. Here's the data of Y_L rounded to three decimals:

0.102 16.977
0.115 16.071
0.129 15.016
0.145 13.781
0.162 12.529
0.177 11.476
0.197 10.184
0.215 9.156
0.232 8.351
0.252 7.492
0.271 6.749
0.289 6.167
0.306 5.645
0.322 5.232
0.348 4.669
0.374 4.238
0.412 3.799
0.459 3.451
0.511 3.185
0.587 2.923
0.659 2.757
0.732 2.634
0.819 2.527
0.917 2.443
1.051 2.360
1.187 2.298
1.324 2.258
1.482 2.214
1.652 2.193
1.832 2.180
1.953 2.173

[Anonymous No.10446095]

>>10445968
Thank you, cheers!

[Anonymous No.10446098]

>>10446058
>is it really normal to write "the derivative of f with respect to [something]" as f∘[something]
That's not what the notation means.
[math] a \circ b[/math] can be read as "a after b". Your functions are single-argument functions, the derivative, when written f', is always with respect to that argument. So [math] f' \circ g[/math] means "the derivative of f, applied to the value of (g applied to the argument)".

[Anonymous No.10446154]

>>10446081
>>10446039
thanks bro's, was already trying that one out after I sent my reply so that's why I wasn't replying. It's unfortunately putting both variables in the same column though, whichever format I'm using.

Should I now replot it in excel so it has all values for x (I used like 20 to plot it) or how should I extract a precise y value for any given x value?

[Anonymous No.10446164]

>>10446020
hmm, it's in a pdf but I can zoom in without losing quality. Does this indicate it's extractable as is?

[Anonymous No.10446168]

>>10446098
Thanks anon. I think my confusion was partially a result of the course telling me to "differentiate f with respect to /something/" as a mental shortcut for the chain rule, and partially my programming background encouraging me to see "f(g(x))" as "actually evaluate n=g(x) and then evaluate f(n)", rather than just writing down the combined rules.

[Anonymous No.10446193]

>>10445611
Sweet.

[Anonymous No.10446254]

>>10446154
>It's unfortunately putting both variables in the same column though, whichever format I'm using.

What do you mean, both variables? if you configure it like >>10446081, it gives you x, y pairs. You need to set a window so only one curve is captured, then export those values.

[Anonymous No.10446266]

>>10446254
it puts both variables in the same column instead of 2 columns

[Anonymous No.10446286]

>>10446266
So either replace those spaces with commas or colons (or whatever excel uses by default as delimiter), or set the field delimiter to space when importing the data. Have you never done this before? Serious question.

[Anonymous No.10446287]

>>10443483
any europeans in?

[Anonymous No.10446292]

What's a good equation for estimating how long would an isolated population of genetically unrelated humans survive?

I have found an equation which states that the live span in generations is 1.5 times the starting population. However it conflicts with the estimation of a population of 160 lasting 4 generations by John Moore, and the estimation of a population of 50 for the same time by Franklin and Soule.

[Anonymous No.10446293]

>>10446287
I think so, why do you ask?

[Anonymous No.10446299]

>>10446292
Maybe you can use approximations for gene defects introduced by close relation mating and come up with an estimate that way?

[Anonymous No.10446367]

>>10446293
see >>10443483

[Anonymous No.10447159]

This is probably an ultra-brainlet question, so feel free to call me a retard if I'm missing some really simple answer.
Why can't the alternating series test function as a test for divergence? I've seen it said that if a series doesn't pass the alternating series test, then it's not necessarily divergent, but I can't find anything explaining why.
The test for divergence states that if the limit of the inner function, as n approaches infinity, either doesn't exist, or is zero, then the series is divergent. Since every alternating series incorporates (-1)^n, wouldn't it always stand that the limit wouldn't exist, and would make the series divergent by the test for divergence?

[Anonymous No.10447347]

>>10447159
The divergence test tells that if the limit of the sequence in the series either doesn't exist or isn't zero, then the series must diverge.
>Since every alternating series incorporates (-1)^n, wouldn't it always stand that the limit wouldn't exist
If that were true then every single alternating series would diverge, and we wouldn't need the AST. Keep in mind that the alternating series has the form [math]\sum^{\infty}_{k=1} (-1)^{k} a_{k}[/math]. I think you are trying to apply the property of the product of two sequences that states that [math](\lim_{k \rightarrow \infty} a_k)(\lim_{k \rightarrow \infty} b_k) = (\lim_{k \rightarrow \infty} a_k b_k)[/math]. But keep in mind that only applies when the limits of both sequences exist. In this case the limit of [math](-1)^{k}[/math] doesn't exist so you can't conclude anything about the limit of the product. It can happen that the limit of [math]a_{k}[/math] goes to 0, in which case the limit could still exist and thus it could still converge. In fact that's the case you are interested in, according to the alternating series test: when the limit of the inner sequence is 0.

Regarding why it can't be used to test for divergence, think about this. The AST requires that the sequence converges to 0 AND is decreasing. Take any sequence that meets these properties, and it will converge. Now pick any two elements of the sequence, and swap them. Since the sequence was decreasing, after swapping the larger element will be surrounded by smaller elements, so you break that monotony. The sequence is still basically the same, and so will be the sum, but now the sequence technically doesn't meet the conditions so the AST can't be applied, yet the sequence still converges to it's prior sum.
The monotony is required to prevent stuff like constant subsequences from showing up and messing up the convergence, but it's too strong a condition so it accidentally filters out series that do converge as well.

[Anonymous No.10447362]

>>10447347
Also fucked up in
>The monotony is required to prevent stuff like constant subsequences from showing up and messing up the convergence
A constant subsequence other than the 0 sequence can't show up because otherwise the limit wouldn't even exist in the first place. It should be in case a convergent sequence of a non-convergent series shows up as a subsequence, for example a harmonic subsequence.

[Anonymous No.10447398]

>>10447347
>>10447362
>I think you are trying to apply the property of the product of two sequences that states that (limk∞ak)(limk∞bk)=(limk∞akbk). But keep in mind that only applies when the limits of both sequences exist. In this case the limit of (−1)k doesn't exist so you can't conclude anything about the limit of the product. It can happen that the limit of ak goes to 0, in which case the limit could still exist and thus it could still converge.
Yep, that's where I was confused. Wound up assuming the limit of (-1)^n not existing would apply to the entire thing. Thanks anon, the explanation helps a lot.

[Anonymous No.10447555]

Hi /sci/, I'm in intermediate algebra at a CC and there is something about radicals and absolute value that I still can't grasp

So I know that

[math] \text{For any real number a, } [/math]
[math] \sqrt{a^2} = |a| [/math]
[math] \sqrt{(x+5)^2} = |x+5| [/math]
[math] \sqrt{(2x-3)^2} = |2x-3| [/math]

But then we started dealing with radical equations and I don't know why this doesn't seem to apply anymore, for example here

[math] (2x-3)^2 = 11 [/math]
[math] 2x-3 = \pm \sqrt{11} [/math]

I understand the right side, but I don't get why we no longer put absolute value bars on the left side.

Thanks for your help.

[Anonymous No.10447615]

I'm designing a small offgrid PV hydroponics garden. It's growing Arugula, a micogreen, and I'm expecting a grow area of around 4m2 from a 5kWp solar array.

I want to keep costs to a minimum, is there a way I can keep this fully DC and scale up an 18650 battery system to be like 12s at 3.7V = 44.4V or something.

I basically want to avoid a costly inverter

[Anonymous No.10447643]

Hello /sci/ I have a melting pot of abstract thoughts and concepts just floating around in my mind. However these ideas are incomplete. I try to use my inner monologue to complete and decipher this mess in my head, but I feel like these thoughts are too complicated to convert into words. As if information will be lost if I attempt to do so. Like describing color to the blind.

The only way I think I can solve my dilemma is just sit and let my mind race. However I don't have think I can achieve much by just relaxing. I feel like I need to completely dull all my senses. Hearing, touch, sight, etc. Only focus on one thing my mind. What is the best way of doing this? Is there some kind of drug? A tank full of salt water? Blindfold and earplugs?

Tl;dr I want to shut off all sensory input to help me think. Temporary of course.

[Anonymous No.10447723]

>>10447555
There's no difference.
[math] x = o^2 \Leftrightarrow \sqrt{x} = |o| \Leftrightarrow \pm \sqrt{x} = o[/math]