/sqt/ stupid questions thread

[Anonymous No.9800402]

This thread is for questions that don't deserve their own thread.
>give context
>describe your thought process if you're stuck
>try wolframalpha.com and stackexchange.com
>How To Ask Questions The Smart Way http://www.catb.org/~esr/faqs/smart-questions.html

prev >>9780216

[Anonymous No.9800654]

>>9800402
Can amoeba get cancer?

[Anonymous No.9800655]

if you leave a cup of water out for a while, what would one expect the highest temperature of a water molecule in the cup - lowest temperature of a water molecule in the cup to be?

[Anonymous No.9800658]

What does the F in:

\left\{\left\{y\to \left(\{x\} \to c_1 \, _1F_1\left(-\frac{b c}{4};a+\frac{1}{2};\frac{x^2}{b}\right)+i^{1-2 a} c_2 b^{\frac{1}{2} (2 a-1)} x^{1-2 a} \, _1F_1\left(-a-\frac{b c}{4}+\frac{1}{2};\frac{3}{2}-a;\frac{x^2}{b}\right)\right)\right\}\right\}

denote?

[Anonymous No.9800660]

>>9800658
context?

[Anonymous No.9800663]

>>9800658
https://en.wikipedia.org/wiki/Generalized_hypergeometric_function#The_series_1F1

[Anonymous No.9800695]

Should I go to Arizona State University or Northern Arizona University to get a BS (bullshit) in Biochemistry?

[Anonymous No.9800697]

Where can I find more great HQ images like this of all the metals? They are so beautiful.

[Anonymous No.9800698]

I would like to start studying medicine, epidemiology, etc.

To those of you that are studying it, or are into it, could you offer some advice?

[Anonymous No.9800715]

How does straighr sex work? How do they decide whose the guy, and whose the other guy?

[Anonymous No.9800725]

>>9800402
I've been out of university for a while... Want to do a sex game that revolves around finding a needle In a haystack kind of problem... But I'm struggling on remembering the math behind the odds and don't know what to Google.

Say I have 1 winning token in a jar of n tokens. You pull one token per day. I want to know the probability of pulling the winning token by day X (or the opposite, how many tokens to include to have a probability of Y by day X).

I feel like this involves the median and std deviation, but I can't put it together.

I tried doing the sum of the odds of each day (Ie, for 22 tokens: 1/22 + 1/21 + 1/20... Continuing the series for the number of days of interest), but I got 25 percent odds on day 5 - which seems wrong intrinsically

[Anonymous No.9800891]

How do I show
[math] \delta (x) = \lim_{\epsilon \rightarrow 0^+} \frac{1}{2} \epsilon |x|^{\epsilon - 1} [/math]
(equation (35) on http://mathworld.wolfram.com/DeltaFunction.html)?
I tried Fourier Transform and [math]\int \delta (x) f(x) dx = f(0) [/math] but I couldn't do it with either...

[Anonymous No.9800925]

>>9800891
Which part of it do you have a problem with:
showing that the limit is 0 for every x != 0, or
showing that the integral over all reals is 1?

[Anonymous No.9800927]

Hi, brainlet here.

Prove that [math]|\sin(t)|^{-1/p}[/math] is of weak [math]L^p(\mathbb{T})[/math]-type. Definition: [eqn]|\{t:|\sin(t)|^{-1/p}\leq \lambda\}|\geq 2\pi -C\lambda^{-p}[/eqn] for some [math]C[/math] and all [math]\lambda>0[/math], or equivalently (the one that I tried to use):
[eqn]|\{t:|\sin(t)|^{-1/p}\geq \lambda\}|\leq C\lambda^{-p}[/eqn]
I tried: if [math]|t|\leq \lambda^{-p}[/math], then
[eqn]|\sin(t)|^{-1/p}\geq |t|^{-1/p}\geq \lambda[/eqn]But this only shows that [math]|\{t:|t|^{-1/p}\geq \lambda\}|\leq |\{t:|\sin(t)|^{-1/p}\geq \lambda\}|[/math], but I want the reverse inequality.
I also tried [math]\frac{2}{\pi}|t|\leq |\sin(t)|[/math] to obtain [math]|\{t:|\sin(t)|^{-1/p}\geq \lambda\}|\leq |\{t:K|t|^{-1/p}\geq \lambda\}|[/math] with [math]K[/math] some constant, but this only holds for [math]|t|\leq \frac{\pi}{2}[/math], so I cannot prove anything for the other [math]t[/math].
Chebyshev/Markov doesn't work either, since you need it to be in [math]L^p(\mathbb{T})[/math], while it's not.

Help me out pls. Thanks

[Anonymous No.9800935]

>>9800654
No. Cancer only happens in multicellular organisms: one cell multiplies uncontrollably opposed to the others while it's not supposed to. An amoeba is singlecellular, so it is can't get cancer. (Not a biologist, but my answer makes completely sense to me.)

[Anonymous No.9800936]

>>9800925
The latter
But integrating over all reals alone does not show a delta function
I either need to show that the Fourier transform is 1 or that the integral over all reals of this expression times f(x) is f(0), in both cases taking the limit of epsilon to 0

[Anonymous No.9801134]

Can urine be used to grow/culture bacteria?

[Anonymous No.9801147]

Nobody wanted to help with my question in the last thread so here it is again:


The definition of open sets depends on which topology we use when defining a topological space. So the definition of continuity using open sets naturally depends on what topology we use to define open sets. Does the epsilon-delta definition of continuity we learned for real numbers also hold true for any topology defined on the reals, or just the standard topology?

[Anonymous No.9801193]

how does he know? what is the computation to be done?

[Anonymous No.9801216]

>>9800725
The chance of an event happening after successive trials is the complement of it not happening by then:
P(A) = 1-P(!A)
The chance of it not happening is if it fails the first, and the second, and the nth time:
P(!A) = P1 * P2 * ... * Pn.
Thus,
P(A) = 1-p^n, if p is the probability of it happening and is constant.

[Anonymous No.9801231]

>>9801193
Not willing to grind by hand or open mathematica, but I suspect they are degenerate and have the same eigenvector.

[Anonymous No.9801232]

>>9801193
If you plug in 4 into the characteristic equation you only get a single value, rather than two.

[Anonymous No.9801254]

>>9801232
do you mean getting v from (A-4I)v=0?

[Anonymous No.9801270]

>>9801254
Yeah that's it. Even though there are "two" eigenvalues of 4, they both correspond to the same eigenvector, so the dimension of that eigenspace of eigenvalue 4 is 1.

[Anonymous No.9801714]

Does anyone know if there is a standard for generalized dates? For example does "late 15th century" academically refer to a specific defined period of time? Or is it just a vague expression that's definition changes depending on who uses it?

[Anonymous No.9801777]

How is gravity's acceleration of a body calculated?

[Anonymous No.9802100]

How are resultant forces possible with newtons 3rd law?

[Anonymous No.9802105]

>>9801777
g(acceleration) = (M(mass of said body)*G(gravitaional constant, look it up!))/r(distance/radius from said body)

[Anonymous No.9802117]

>>9801714
generally in history for a period to get a title like that it needs to mark a start or end of event(s)

[Anonymous No.9802132]

>>9802105
as in 6.67408e-11*5.97219e24/6.371e6?
i was trying to get earth's 9.81 m/s2

[Anonymous No.9802153]

>>9800655
Lowest 0 degrees, but only for an instant between collisions. Highest is thought to tell. Not that high.

[Anonymous No.9802187]

How do I prove this: https://proofwiki.org/wiki/Rational_Points_on_Graph_of_Sine_Function

[Anonymous No.9802209]

ok, maths whizzes, please help
I learnt that there is (x^3)^3 where it is x^9 or x^27 depending on the height of the exponent outside of the bracket. What is the name for this? 'Exponent height' didn't bring up anything

[Anonymous No.9802218]

>>9802209
Double exponent

[Anonymous No.9802234]

What is the required knowledge to understand particle physics?
I'm studying ChemE but I'd like to learn about high energy physics just for fun.

[Anonymous No.9802465]

>>9802218
thanks

[Anonymous No.9802479]

>>9802209
> I learnt that there is (x^3)^3 where it is x^9 or x^27 depending on the height of the exponent outside of the bracket.
(x^3)^3 = x^9
x^(3^3) = x^27

If you see it as 2 levels of superscript without any brackets, it's the latter.

[Anonymous No.9802578]

>>9800402
hypothetically (ignoring capacitance), can a transistor switch at higher frequency than its bandgap

[Anonymous No.9802629]

Why isn't the world covered in 5000 feet of fingernails and hair?

[Anonymous No.9802635]

>>9802629
because keratin is biodegradeable

[Anonymous No.9802643]

>>9802635
By what?

[Anonymous No.9802646]

>>9802643
microorganisms and other creatures, it's just not digestible by humans and weak ass mammals

[Anonymous No.9802692]

>>9801777
>>9802132
bump
needs further explanation

[Anonymous No.9802765]

Any medfags here? I am curious what would happen if a girl about 20 years old had her spine severed with a scalpel in a post-apocalyptic situation, in a dusty hospital but using alcohol to sanitize it, basically if someone who knew what they were doing did it but didn't have modern sterilization techniques. And the spine was severed with the intent to make her unable to walk.
>which vertebrae would be most likely to be done to? I figured L2.
>what kind of spinal infection would be most likely, and how fatal would it be?
>how long would it take the girl to die from the spinal infection and what would the symptoms be?
>how would bowel / bladder / sexual function be affected? An anon last thread said it wouldn't be. But I'm just adding that back in.
Basically the story here is that I really like post-apocalyptic genre so I ran a TTRPG campaign for it, and one player captured a female bandit leader and instead of killing her, he cut her spinal cord and rolled really well on the surgery skill check (which for some reason he had). So they brought her back to their village in a wheelchair and since he was such a fucking edgelord I feel like I should describe her death from spinal infection in the most graphic and stomach-turning way possible and make him feel bad for what he did. So any gruesome details I can be given would be good.

[Anonymous No.9802937]

>>9800402
CS brainlet here, learning some topology and measure theory. I had this question a while ago but ignored it.

When do you ever take more than countably many unions/intersections?

[Anonymous No.9803059]

In the second equation, for displacement, why is at^2 divided by 2?

This is for a ball being thrown vertically.

[Anonymous No.9803062]

>>9803059
if you integrate v0+at by time you get v0t+at^2/2

[Anonymous No.9803082]

>>9802937
never, that shit's only defined up to countability.

uncountable sets are basically impossible to work with directly

[Anonymous No.9803085]

>>9801193
take [math]A-4I[/math] and verify the column space is dimension 1 you dolt

[Anonymous No.9803086]

>>9801231
That's literally the definition

[Anonymous No.9803091]

>>9803062
Thank you. I am such a brainlet.

[Anonymous No.9803101]

>>9802937
Say you have a collection of functions f_t for t in some uncountable index set T (for example, the real numbers). Then the set {x: sup_t f_t(x) < c} can be expressed as uncountable intersection of the sets {x : f_t(x) < c}.

[Anonymous No.9803116]

>>9803101
Thanks!

[Anonymous No.9803189]

>>9802105
>>9802132
it's r squared

[Anonymous No.9803212]

I don't get why h is assumed to be continuous or why h prime is what it is. Nothing after h(a) = 0 = h(b) is clicking. Thank you all.

[Anonymous No.9803271]

>>9803212
I hope you've been able to figure out by yourself in these past 30 minutes. If not:
The reason we take such an [math]h[/math] is that Rolle's theorem allows to link [math]h[/math] and its derivative on at least a point.

[math]f'[/math] and [math]g'[/math] both exist on [math]]a,b][/math], which means that [math]f[/math] and [math]g[/math] are both continuous on that same interval. As such, [math]h[/math] is continuous on [math]]a,b][/math] as the difference of such functions.

Now we have to show that [math]h[/math] is continuous on [math]a[/math].
[eqn]h(a)=f(a)-\frac{f(b)}{g(b)}g(a)=0-0=0 [/eqn]
and
[eqn]\lim_{x \to a, x>a}h(x) = \lim_{x \to a, x>a}f(x)-\frac{f(b)}{g(b)}g(x)=0-0=0[/eqn]
Therefore, [math]h[/math] is continuous on [math][a,b][/math]. Then, you can derive [math]h[/math] on [math]]a,b[[/math] as the difference of two such functions (f and g). For the derivative, you have a difference of two functions, one multiplied by a constant, so nothing fancy there.

You simply apply Rolle's theorem to find the aforementionned link. For the final line, since a<x<b, when you have b go towards a, x has to go towards a as well.

I hope that's somewhat clear.

[Anonymous No.9803286]

>>9801147
Can someone please help me with this question or not? I will rephrase what I'm trying to say.

We often say and prove that the definition of continuity in which the inverse image of open sets is always an open set for continuous functions is equivalent to the typical epsilon-delta definition one typically encounters in a real analysis class. My question is are these definitions equivalent for any arbitrary topology on the real numbers or only for certain topologies (like the standard topology)?

[Anonymous No.9803292]

Consider 3 objects. Is the center of mass of the three objects the same as the center of mass of the center of mass of two of the objects and the third object?

[Anonymous No.9803295]

>>9803292
Is two objects and a third not literally the exact same mass as three objects?

[Anonymous No.9803297]

>>9803295
I want a proof of the associative property of the center of mass

[Anonymous No.9803309]

>>9800654
Its DNA could probably get damaged to the point where it could behave as a cancerous cell in my body or yours, but it would die rather quickly because it would not have a neighbourhood of cells that could supply it with huge amounts of energy and shelter it, such as when a multicellular organism gets cancer.

[Anonymous No.9803320]

>>9800698
I'm a medfag from Europe.
The workload is pretty large and dumb hardworking people are generally more successful than those who have high intelligence but weak work ethic because of all the memorisation required. If you like helping people/want money/want respect from normies than this is for you and you get to solve puzzles for a living once you finish school.
If I had another chance though I'd go into physics. Nobody told me there would be several times when I would seriously consider suicide.

[Anonymous No.9803325]

so i am reading a supposedly scientific paper and there is a calculation going on that i think might be wrong, but maybe it's just me being retarded. pic related.

i need to calculate (1) with matrix (2), where (3) is supposed to be the first row of the result of (1). i calculated (1) with the help of MATLAB and am not able to get the same result. here is what i did:

G=[0.033 0 0 0 0 0; 0.128 0.033 0 0 0 0; 0.272 0.128 0.033 0 0 0; 0.452 0.272 0.128 0.033 0 0; 0.654 0.452 0.272 0.128 0.033 0; 0.863 0.654 0.452 0.272 0.128 0.033];

((transpose(G)*G + 0.1 * eye(6,6))^-1) * transpose(G);

how retarded am I?

[Anonymous No.9803361]

>>9803297
If you have a collection of weighted points [math]((A_i,\alpha_i))_{1\leqslant i\leqslant n}[/math], then the center of mass [math]G[/math] is defined as the only point for which
[eqn]\sum_{i=1}^{n}\alpha_i\overrightarrow{GA_i}=\overrightarrow{0}[/eqn]
Which is equivalent to:
[eqn]\sum_{i=1}^{n}\alpha_i(A_i-G)=\overrightarrow{0} \iff \sum_{i=1}^{n}\alpha_i A_i=\sum_{i=1}^{n}\alpha_iG \iff G=\frac{1}{\alpha_1+\dots+\alpha_n}\sum_{i=1}^{n}\alpha_i A_i [/eqn]
The theorem you want to prove is that given a collection of weighted points [math]((A_i,\alpha_i))_{1\leqslant i\leqslant n}[/math], if [math]G[/math] is their center of mass, then [math]G[/math] is also the center of mass of [math](H=Bar_{1\leqslant i \leqslant k}(A_i),\alpha_1+\dots+\alpha_k)[/math], and the remaining points [math](A_{k+1},\alpha_{k+1}),\dots,(A_{n},\alpha_{n})[/math], where [math]\sum_{i=1}^{k}\alpha_i\neq0[/math] and [math]\sum_{i=k+1}^{n}\alpha_i\neq0[/math].
All we have to do is calculate:
[eqn](\alpha_1+\dots+\alpha_k)H+\sum_{i=k+1}^{n}\alpha_i A_i=(\alpha_1+\dots+\alpha_k)*\frac{1}{\alpha_1+\dots+\alpha_k}\sum_{i=1}^{k}\alpha_i A_i+\sum_{i=k+1}^{n}\alpha_i A_i[/eqn]
You then end up with:
[eqn](\alpha_1+\dots+\alpha_k)H+\sum_{i=k+1}^{n}\alpha_i A_i=\sum_{i=1}^{n}\alpha_i A_i[/eqn]
By dividing by the new total weight, [math](\alpha_1+\dots+\alpha_k)+\alpha_{k+1}+\dots+\alpha_n[/math], you end up finding that the center of mass of your two new points is equal to G.

[Anonymous No.9803365]

>>9803361
Welp, I messed up on the TeX but I hope you get it

[Anonymous No.9803383]

I'm writing a paper and claim that the media coverage about a certain topic increased around a certain time.
Is there a easy way for me to see how many articles with a certain keyword were published in a certain time? Can I somehow easily search that?
I mean I can show how interest in google keywords changed but that doesnt prove that the media coverage did as well.

[Anonymous No.9803410]

>>9803361
thank you

[Anonymous No.9803417]

>>9803361
is (A_i - G) the distance between the point and the center of mass?

[Anonymous No.9803441]

>>9803417
[math]\overrightarrow{GA_i}[/math] is the vector that goes from point G to point A_i, which corresponds to the difference between both points.]

[Anonymous No.9803444]

Need help with very basic general topology. I was supposed to prove this:
Let [math] (X, \tau) [/math] be a topological space. If every [math] x \in X [/math] has a local base [math] B_{x} [/math] in X, then [math] B = \bigcup \{ B_{x} : x \in X \} [/math] is a base in X.

My proof:

Lemma (*) A family [math] B \subset \tau [/math] is a base in X if and only if for every [math] x \in X [/math] and for every neighborhood N of x, there is [math] \beta \in B [/math] such that [math] x \in \beta \subset N [/math].

Let X be an element of X and N be a neighborhood of x. Then there is some open V such that [math] x \in V \subset N [/math]. Since x has a local base [math] B_{x} [/math] in X and [math] x \in V [/math], then there is [math] \beta \in B_{x} [/math] such that [math] x \in \beta \subset N [math].

Then I was going to prove [math] B_{x} \subset B [/math] and use (*) to conclude B is a base in X, but I realized I just proved any local base of x is a base in X, which means I royally fucked up somewhere. Problem is, I don't know where.

[Anonymous No.9803447]

Need help with very basic general topology. I was supposed to prove this:
Let [math] (X, \tau) [/math] be a topological space. If every [math] x \in X [/math] has a local base [math] B_{x} [/math] in X, then [math] B = \bigcup \{ B_{x} : x \in X \} [/math] is a base in X.

My proof:

Lemma (*) A family [math] B \subset \tau [/math] is a base in X if and only if for every [math] x \in X [/math] and for every neighborhood N of x, there is [math] \beta \in B [/math] such that [math] x \in \beta \subset N [/math].

Let X be an element of X and N be a neighborhood of x. Then there is some open V such that [math] x \in V \subset N [/math]. Since x has a local base [math] B_{x} [/math] in X and [math] x \in V [/math], then there is [math] \beta \in B_{x} [/math] such that [math] x \in \beta \subset N [/math].

Then I was going to prove [math] B_{x} \subset B [/math] and use (*) to conclude B is a base in X, but I realized I just proved any local base of x is a base in X, which means I royally fucked up somewhere. Problem is, I don't know where.

[Anonymous No.9803474]

How do I determine the equation of a helix/sinusoid given inital and final conditions? I know it's radius is 5 and z(0)=5, z(f) =15 and it passes through 435° in that time.

[Anonymous No.9803602]

I'm looking for the name of an anglo scientist (probably evolutionary psychologist or something like that) that is in his 30s I guess, white, wears glasses and turtlenecks with sports jackets and published something (I think with several other authors) about IQ evolution if I remember correctly, around 2015-16.

[Anonymous No.9803610]

Has [math] \LaTeX [/math] stopped working here?

[Anonymous No.9803620]

>>9803447
So, in case anyone is wondering, on my way to school I realised my mistake. I didn't prove any local base of x is a base in X because what I found was one family of open sets for each x when (*) states I need one family for all x.

[Anonymous No.9803890]

Brainlet tier electrical engineering question:

If an electrical device that is rated for a certain voltage and current is connected to a source that has the same voltage but lower current, how does that affect its operation? Is there a risk of damage?

If I try to charge a battery that way, will it be charged to full capacity?

I'm inclined to think that going lower than rated is at least safe, but electicity is fucking sorcery to me so I can't be sure.

[Anonymous No.9803913]

>>9803286
Not a real mathfag, just a physics student but i'll take a shot. Wouldn't it work for all topologies because the manifold should locally look like Rn regardless of the topology?

[Anonymous No.9803920]

>>9803890
Current is closely related to power by P=I^2 R, so less current means that anything which draws energy (heating, motor, etc.) will have less energy per second for use. Charger should still work but it will take longer.

[Anonymous No.9803923]

>>9803913
It doesn't just have to look like R^n; it is R^n. My question is concerning R^n, do different topologies of R^n still all match the epsilon-delta definition of continuity or only certain ones?

[Anonymous No.9803929]

X is a satellite in a uniform circular motion around the earth. What is the direction (1,2,3) of the resultant force on the object, or is the resultant force 0?

[Anonymous No.9803939]

>>9803923
>My question is concerning R^n, do different topologies of R^n still all match the epsilon-delta definition of continuity or only certain ones?
Have you tried adapting the proof?

[Anonymous No.9803943]

>>9803929
what have you tried?

[Anonymous No.9803945]

>>9803929
>is the resultant force 0?
The resultant force is non-zero, because the velocity changes (although the speed doesn't; velocity is a vector quantity). If the velocity changes, the momentum changes (momentum is also a vector quantity), and then by Newton's second law there has to be a resultant force on the object equal to the rate of change of momentum.

>What is the direction (1,2,3) of the resultant force
The way to get this is to consider the satellite at two instants separated by a small time interval. The velocity vector will remain tangential to the circle, and the speed (the magnitude of the velocity vector) remains constant. If you perform vector subtraction with these, you can get the direction vector of the velocity change, which is the direction vector of the momentum change, which by Newton's second law has to be the direction vector of the force.

[Anonymous No.9803948]

>>9803923
The epsilon-delta definition presumes the existence of a metric. For metric spaces, you can generate a topology by defining open sets as the union of open balls. In that topology, the epsilon-delta definition will be equivalent to the general definition; in other topologies, that need not be the case.

[Anonymous No.9803954]

>>9803948
Thank you. This answered my question perfectly well. My confusion came from in Rudin and many other books, theories often state "Let X be a topological space" but every set CAN be a topological space, even just trivially, so I was confused why they would state that. But now I think it means that the following theorem will be true for at least some topology defined on the set X, as opposed to any arbitrary topology defined on the set X. Thanks.

[Anonymous No.9803962]

>>9803943
>>9803945
I figured since it's in "uniform motion" the force would automatically be 0. However the correct answer is 3 (towards Earth).

> If you perform vector subtraction with these

What these? The two vectors taken at two very close intervals?

[Anonymous No.9803963]

>>9803954
>But now I think it means that the following theorem will be true for at least some topology defined on the set X, as opposed to any arbitrary topology defined on the set X
If the proof of the theorem uses only purely topological properties of the open sets, then it would indeed hold for arbitrary topologies.

[Anonymous No.9803966]

>>9803963
Specifically this was my question, which I asked on stack exchange:
https://math.stackexchange.com/questions/2812075/why-do-mathematicians-refer-to-sets-as-topological-spaces-or-measurable-space

[Anonymous No.9803969]

>>9803189
sweet

[Anonymous No.9803980]

>>9803966
>https://math.stackexchange.com/questions/2812075/why-do-mathematicians-refer-to-sets-as-topological-spaces-or-measurable-space
They mention that Y is a topological space because they are implicitly implying that it is made into a measurable space by giving it the Borel algebra.

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

[Anonymous No.9803989]

>>9803954
>But now I think it means that the following theorem will be true for at least some topology defined on the set X, as opposed to any arbitrary topology defined on the set X
no, it means that it's true for any topology on X. consider this:
>let G and H be groups and let f: G -> H be a group homomorphism. then f(G) is a subgroup of H.
surely every set G can be endowed with a group structure, do you feel that this theorem is true only for SOME group structures on G or for all of them ?

[Anonymous No.9803991]

>>9803989
>surely every set G can be endowed with a group structure
This is false.

[Anonymous No.9804000]

>>9800402
how far away from reality is an iron man suit
most notably the propulsion technology

[Anonymous No.9804009]

>>9803980
Ah ok. I see what you're saying now. Thank you.
>>9803989
Ok, so we are picking a fixed topology, even if it is unspecified, simply because it is important that we specify that we are using a specific topology, even though the theorem would work regardless of which topology we pick. I think I understand the nuance and importance of doing that now.

[Anonymous No.9804038]

In linear algebra, what exactly is the difference between least squares method and the term "energy minimization"? I

[Anonymous No.9804221]

Is the middle line supposed to read [eqn]
\frac{\partial \Psi}{\partial y_i} - \frac{d}{dx} \left( \frac{\partial \Psi}{\partial y'_i} \right) \equiv 0,
[\eqn]?
and if not, what the fuck does it mean?

[Anonymous No.9804253]

>>9804221
No, an extra line in the equal sign just means that the two things are *really* equal. Like 50% more equal than regular equal.

[Anonymous No.9804257]

>>9804221
My guess would be
[math]
\partial_{y_i} \partial_{y'_i} \psi - \frac{d}{dx}\partial_{y'_i}\psi=0\\
[/math]
but I'm too tired to see if it's correct

[Anonymous No.9804261]

>calculate x(t) from the given Hamiltonian for a given x(0) and p(0)

Im officially lost. How do I solve this? Any way that I solve for x, I end up with it being dependent on p.

[Anonymous No.9804268]

>>9804261
Hamilton equations
[math]\dot p= -\frac{\partial H}{\partial x}\\
\dot x = \frac{\partial H}{\partial p}
[/math]

[Anonymous No.9804270]

>>9804257
I'll see if this works. thanks anon.

[Anonymous No.9804275]

>>9804257
hmm actually no I think it's what I originally posted since it says it leads to the same system of Euler equations, which of course have that form.

[Anonymous No.9804286]

>>9804253
This guy is essentially correct. Some authors prefer using three lines in the equal sign to denote that two functions are equal for all input values, and not just for some specific point x. Here the authors are telling you that the left hand side is equal to the function that always returns 0.

Of course this notation is completely redundant and only brainlets are using it.

[Anonymous No.9804306]

>>9804286
Right I realise that, but that's not what I was really asking about. I was asking about why the partial derivative operator, and the partial derivative of Psi appeared in the same line.
To my knowledge, you would rarely write something like
[eqn]\frac{d}{dx} + y(x)[/eqn]
but you might write
[eqn]\frac{dy}{dx} + y(x)[/eqn]
or
[eqn](\frac{d}{dx} + 1 )y(x)[/eqn]
so I was asking because I wasn't sure if that was something I hadn't seen before and didn't know its meaning, or if it was a misprint.

[Anonymous No.9804321]

A good book to self teach data structure? Something easy to read if possible. I'm kind of a brainlet.

[Anonymous No.9804322]

>>9804268
Yeah I know those two. Are there any more of these that I need to know for this question?

[Anonymous No.9804377]

>>9804261
>Im officially lost. How do I solve this? Any way that I solve for x, I end up with it being dependent on p.
I've not tried this problem so I'm not sure if it'll work, but usually you'd find p from the Lagrangian and substitute it in to eliminate p then solve the differential equation for x.

[Anonymous No.9804397]

Is there anything beyond the known Electromagnetic Spectrum? Are their wavelength smaller than Gamma or longer then Radio?

[Anonymous No.9804439]

>>9804397
To my knowledge, there aren't names for EM radiation higher energy than gamma rays, or lower than radio waves, but presumably extremely long wavelength radio waves exist (possibly on the scale of the universe) and extremely energetic gamma rays presumably exist. Gamma rays become more and more transparent to matter as energy increases, so it would be very difficult to detect very energetic gamma rays. A theoretical lower limit on the wavelength of a gamma ray could be the planck length, which would be extremely high energy and almost completely transparent to normal matter. Again, extremely long wavelength radio waves would also be effectively impossible for us to detect.

[Anonymous No.9804473]

Is it possible to become better if we're talking about logical tasks? I've been unable to solve easiest of them (tried competitive programming), it's like I cannot hold more than a few pieces of information in my head. When my friends are able to solve them quite easily (they succeeded in job interviews, they help me if I ask them how to solve something but I still do not understand their solutions), I fail repeatedly.

I am losing hope, anons. What should I do? In my definition smart people are those who is able to get the "essence of things", and not simply memorize, smarter ones are those who do it relatively fast, and the smartest are able to come up with unique solution or have the top-notch efficiency.

[Anonymous No.9804476]

>>9804473
To add, I do really struggle even with normal learning. I thought about flunking out after first year of CS, where I could pass everything without any significant effort. Now I simply getting by with luck and university mates help.

[Anonymous No.9804477]

When talking about the power method in a PageRank algorithm, what is the application of the adjacency matrix multiplied with the transposed matrix, seen in the pic related?

[Anonymous No.9804487]

How does an AM work?

[Anonymous No.9804584]

>>9802187
Help

[Anonymous No.9804861]

would something similar to this actually work
yes or no

[Anonymous No.9804891]

>>9804322
[eqn]
\dot p = -\omega^2x-2\omega^2\lambda x(\frac{p^2}{2}+\frac{\omega^2x^2}{2})=-\omega^2 x(1+\lambda (p^2+\omega^2 x^2))\\
\dot x = p+2p\lambda (\frac{p^2}{2}+\frac{\omega^2x^2}{2})= p(1+\lambda( p^2+\omega^2x^2))
[/eqn]
Now you either do some [math]\lambda \approx 0[/math] magic or try legendre transform it into langrangian to try some lagrange multiplier stuff I guess?
No idea man

[Anonymous No.9804930]

>>9804891
Just Legendre Transform to Lagrangian, then use [math]p = \frac{\partial L}{\partial \dot{x}}[/math].

[Anonymous No.9804942]

>>9804861
I can't tell what it is, but no.

[Anonymous No.9805005]

I'm just starting some work on radiative transfer in local thermodynamic equilibrium. There's a term which I can't quite pin down though, which is:

[math]
\frac{1}{2} \sigma a c T^{4}
[/math]

Is this something to do with black body emission? [math]a[\math] is the radiation energy density constant and [math] \sigma [\math] is, I believe, a scattering cross section.

[Anonymous No.9805025]

>>9804930
How do I do legendre transform to get the lagrangian though?
I know how I get the Hamiltonian from the Lagrangian but not the other way around,

[Anonymous No.9805029]

>>9805025
[eqn]H = \sum_i p\dot{q} - L [/eqn]
right, so just rearrange to
[eqn]L = \sum_i p\dot{q} - H [/eqn]

[Anonymous No.9805038]

>>9804221
Yes they forgot the Psi in the first term. I still don’t get it though. Why is the total derivative of Phi_{yi} with respect to x equal to the partial derivative of the same with respect to x?

[Anonymous No.9805041]

>>9805038
Sorry, I see it now.

[Anonymous No.9805044]

>>9805029
Ok I guess I figured that...
So since I only have one spacial and one momentum variable, its just L = dx/dt p - H right?
So I did that and got an L that looks absolutely hideously not like an L most likely because I made a mistake somewhere...

So now in theory I should be able to get two differential equations by using euler-lagrange, one for x and xdot and one for p and pdot.
However since my L doesnt contain any derivatives, I will just get regular equations that dont contain time at all, so theres no way of getting an x(t) out of this.

[Anonymous No.9805056]

>>9805044
You'll probably need to substitute p using [eqn] \dot{x} = \frac{\partial H}{\partial p} = p + \lambda p \left( p^2 + \omega_0^2 x^2 \right) [/eqn] back into your Lagrangian to get it as an explicit function of [math]\dot{x}[/math]. I know you can't easily solve that expression for p, but you might be able to rearrange the expression for the Lagrangian such that you can just substitute it in and get a nice L in terms of x and [math]\dot{x}[/math]. If not then I don't know what to suggest. As a warning, I tried finding the Lagrangian and I didn't get the same as you (I could easily have made a mistake though).

[Anonymous No.9805073]

>>9805056
>>9805044
Actually, I honestly don't know how to proceed. Are you sure you're supposed to solve it exactly and not treat the lambda term as a perturbation?

[Anonymous No.9805080]

>>9805073
I think he's supposed to do that and that there's no analytical solution for big lambda

[Anonymous No.9805082]

>>9800402
How the fuck did LIGO detect gravity waves?
It's an "L" shaped detector with laser beams and mirrors. OK.
The gravity wave ripples space. Does that make the beam take longer to travel because it must follow the curves of the ripple? Light always travels at the speed of light, so did it need to travel further than if there was no "ripple" ?
How does LIGO work?

[Anonymous No.9805088]

>>9805082
It works on the same principle as a Michaelson interferometer. You take one laser, split it apart with a beam splitter then recombine them later. Due to interference, as you get a small path difference (on the scale of the wavelength of light you're using) you either get constructive interference or destructive interference. So if a gravitational wave is observed, it momentarily compresses space, so that one path becomes slightly shorter than the other, and different interference effects are observed.

Take a look at this video: https://www.youtube.com/watch?v=j-u3IEgcTiQ

Ligo works on the same principle, but rather than moving the mirror, gravitational waves slightly change the path length of one laser relative to the other.

[Anonymous No.9805092]

>>9804891
You can divide the first equation by the second and conclude that [math] p^2 + \omega^2 x^2 [/math] is constant.

[Anonymous No.9805095]

>>9805092
fucking genius

[Anonymous No.9805182]

>>9805082
Thank you. I watched the MIT clip and I'm aware of wave interference. Let's not get into the "measurement problem" just yet.
So, light (laser beams) are sensitive to this compression of space. Because space is the medium of transport and it doesn't make sense to be "insensitive" to the ripple. Therefore "line" of sight is a misnomer. It's not a "line" at all. It's an arc or wave of sight, a twist or some other distortion. Is there a "more true" straight line independent of the fabric of the space we are in?
That requires another dimension? Just spit ballin here. I'm a brainlet.

[Anonymous No.9805185]

>>9805182
was meant for ...>>9805088
and checked.

[Anonymous No.9805203]

>>9805182
>>9805185
>. Because space is the medium of transport and it doesn't make sense to be "insensitive" to the ripple. Therefore "line" of sight is a misnomer. It's not a "line" at all. It's an arc or wave of sight, a twist or some other distortion. Is there a "more true" straight line independent of the fabric of the space we are in?
I'm not 100% sure what you're describing, but light travels along 'geodesics' in spacetime. A geodesic is the shortest line between two points in a particular geometry. For instance in Euclidean 3 dimensional space, the geodesic is simply a straight line between two points (If you're interested in the maths required to prove this look up the calculus of variations.) On the surface of a sphere the geodesic is the great circle between two points, on the surface of a cylinder the geodesic is a helix. Mass causes space-time to become distorted, which for instance causes the geodesic and hence the path of light to curve around very massive bodies like stars and black holes. Because we are so far from the source of gravitational waves, they appear to us as plane waves. You can imagine them as waves of rarefaction and elongation of space-time passing through us and slightly distorting space time so that the length of one of the arms of LIGO becomes slightly shorter than the other.

[Anonymous No.9805228]

>>9805182
>Is there a "more true" straight line independent of the fabric of the space we are in?
>That requires another dimension?
Okay so I reread this and understand what you're asking now. If I go back to the example of a geodesic on a sphere, you can imagine a straight line in 3-dimensions punching through the sphere which is shorter than the straight line. Presumably you're asking if there's a line existing in 4 (spatial) dimensions which punches through the curvature of 3-d space and thereby is shorter than its geodesic. But I'm afraid I can't answer that question. Maybe someone here will be able to answer it, but I'd imagine we would be entering the realm of pure speculation.

[Anonymous No.9805231]

>>9805073
Just got the solution.
Basically the idea is to realize that the first two terms are the hamiltonian for a harmonic oscillator H0 and that the third part is just lambda(H0)^2.
Then, since the entire thing is time independent, for some reason you can say that H0 is also time independent and write p in terms of H0 which eventually lets you solve the entire thing.

My tutor did say that on its own, the question is pretty weird and only makes sense if you also look at the next one, which uses the result from this one to solve another Hamiltonian using a canonical transform.

Im far from actually understanding this though. Will have to sit down some more and do it again on my own...

[Anonymous No.9805235]

Starting kinematics today. Wish me luck. Your favorite unsolved problem in kinematics?

[Anonymous No.9805318]

How much % of end of chapter exercises do you usually do?

[Anonymous No.9805461]

>>9803962
bump

[Anonymous No.9805464]

Where can I find a neat latex resume template?
Every single one I got to via google didn't work in LyX.

[Anonymous No.9805494]

I've been learning programming towards web development for the last two years. I have now three websites up, and I want to learn math so that I can better understand computers and because I think math is interesting.

This is not a question with an objective answer. It is more me asking for advice:

I want to study math, but right now the technology I use to program websites is somewhat slow for development (Django). I know PHP is a nightmare, but I also know that WordPress makes everything faster.

I am torn between resting now from web development and studying math. Web development is for making money. Math is for quality of life.

I am torn between resting from learning further web dev to study math and postponing my math studies so that I can learn this other technology that will make me earn more money.

Help, please. I'm stressed as fuck because I can't decide.

[Anonymous No.9805503]

>>9805494
In your place, I would pick learning math, if that's really what you want to do.

[Anonymous No.9805727]

Noob here with basic knowledge of electromagnetism, i just watched a yt video about the quantum eraser, what the fuck? Is that true? Do electrons know what's happening?

[Anonymous No.9805863]

Can someone explain this? Why is P(A1' n A2') the same of P(none awarded)?

[Anonymous No.9805869]

If I want to prove 0 < a < b => a^(1/n) < b^(1/n), can I use this proof by contradiction? is it correct?

P: 0 < a < b
¬P: 0 < a < b is NOT true
R: a >= b
we have R => ¬P
Q: a^1/n < b^1/n
¬Q: a^1/n >= b^1/n
we know: (1) 0 < a < b => a^n < b^n
assume P and (P => ¬Q)
but (¬Q => R) by using (1) for the exponents: a^1/n >b^1/n, a > 0 => a^1/n > 0 ... => a^n/n >= b^n/n => a >= b
R => ¬P
we now have (¬P and P)
so ((P => ¬Q) => (¬P and P))
(¬(¬P and P) => ¬(P => ¬Q))
so we have ¬(P => ¬Q)
which means (P and Q)
therefore Q


I know that it's easier to prove by proving the contrapositive but I am curious if this is correct

[Anonymous No.9805896]

How do I prove: f := {(x,y) ∈ R^2 :y = sin x}

[Anonymous No.9805911]

>>9800402
Is computer science really such a horrible degree? Is it better to drop it in favor of somthing like physics or math?

[Anonymous No.9805913]

>>9805911
yes

[Anonymous No.9805929]

>>9805913
I'm currently doing math and CS as a double degree. What would be a good replacment for CS, physics or finance maybe?

[Anonymous No.9805948]

>>9805929
ah no forget what I said, math + cs is good, pure math / physics / etc. are overkill unless you know for sure that you can leverage the degree and study some CS and programming in your free time such that you can get specialized jobs (in finance, data science, applied statistics, w/e)

no math at all is bad though, I went through that

by no math I mean, meme math, if you get what I mean

at least know enough math such that you can juggle algorithms, complexities, discrete math, etc.

if you want to rape a field, such as biology, by applying AI / ML / statistics / w/e you wanna call it, then think about what are the requirements, those fields are much easier to get into with a math/physics degree than with cs

[Anonymous No.9805953]

>>9805929
I did the mistake of thinking that I was too stupid for math/physics, not because of /sci/ but because of my own mental memes, so IMHO if you really enjoy math and not want to be a shit-tarded codemonkey and you don't have a good idea for an app/business and don't have enough money, then do more math and try to leverage the fact that you like and are possibly good at math, which is a very rare thing, even among programmers (just check out the interview questions at the big companies)

[Anonymous No.9805957]

>>9805929
if you don't wanna fall prey to the AI meme, which is in a bubble, especially w.r.t. the master's degrees which are cash grabs, then learn your maths, continue your degree or switch to maths or physics and pick a master's such as computational statistics, computational finance, computer vision, etc. but NOT the meme AI master's which are usually pure shit in comparison

[Anonymous No.9805975]

>>9805957
Robotics and autonomous systems, do you reccon that is a meme?
>>9805953
I much prefer studying math over CS classes. Even if its harder in one sense I feel much better doing so because there is more freedom in it. You learn actual concepts but in CS classes it's alot of "do x in the given framework" which might be easy but frustrating.
>>9805948
Ty for tips

[Anonymous No.9805977]

I want to be a Civil Engineer. What courses would be the best to take to transfer?

[Anonymous No.9805987]

>>9805975
>Robotics and autonomous systems, do you reccon that is a meme?
Sorry I don't know about robotics because I didn't read too much about it. I only know about what I was interested in and I didn't want to go into robotics because it seemed to me like math and CS offered the most freedom and employability and lack of stress at work. I mean, just look at the job market, code camps and other disgusting shit actually work from time to time, in the sense that I've seen people with History or Geography degrees hold jobs as full stack devs or better.

I may be biased though, because although I studied CS in the UK, I come from Eastern Europe where robotics is incredibly difficult, rigorous and the teachers give you hell and don't teach you anything. I've heard some really bad horror stories, but I'm sure I'm biased.

[Anonymous No.9806249]

If a square shaped plaque with sides of length [math] l [/math] and a charge density of [math] -\lambda [/math] is placed near an infinite disc of charge distribution [math] \lambds [/math] then does the square plaque behave like a point charge?
I said the square plaque behaved as such in an exam, got all the results correct, and my professor deducted 2 points because she said i cant say that the square plaque behaves like a point charge.
Im genuinely curious, she simply said it didn't and didn't explain exactly why.
To me it makes perfect sense it does.

[Anonymous No.9806284]

>>9805005
It would seem so.
https://en.wikipedia.org/wiki/Black-body_radiation#Stefan%E2%80%93Boltzmann_law

[Anonymous No.9806304]

>>9806249
If I am not mistaken, The infinite plane has an electric field that does not depend on the distance of the plane, as opposed to the electric field of a point charge, that decays with r^2.

[Anonymous No.9806312]

>>9806249
The fact that the plaque is "near" the infinite disc implies that the distance between the two is comparable to the size of the plaque.

To approximate it to a point charge, its size would have to be much less than the distance.

[Anonymous No.9806386]

>>9806304
Yeah im saying the plaque behaves as a point charge, not the plane.
>>9806312
The electric field of an infinite disc does not depend on the distance.

[Anonymous No.9806650]

>>9800402
Am I stupid or is this just worded terribly? I'm supposed to prove this, I looked at the proof but it's too vague. Can anyone provide a clear and detailed proof that will erase any doubt?

[Anonymous No.9806662]

>>9800402
what is frac in >>9795040???
Fraction?

[Anonymous No.9806665]

>>9806662
>Fraction?
Yes.

[Anonymous No.9806668]

>>9806650
>Am I stupid or is this just worded terribly?
It's not worded terribly.

>I'm supposed to prove this, I looked at the proof but it's too vague.
What part is vague?

[Anonymous No.9806685]

>>9806650
Just post a proof, retard. All proofs of it are just plain retarded. It is worded terribly

[Anonymous No.9806721]

>>9806668
Proofs like this are vague https://math.stackexchange.com/questions/453013/backward-induction-tao-analysis-vol-1

There's jumps in the inferences. I'd like to see one without those

[Anonymous No.9806726]

>>9806721
>Proofs like this are vague https://math.stackexchange.com/questions/453013/backward-induction-tao-analysis-vol-1
That's not the proposition you're meant to prove.

[Anonymous No.9806738]

>>9806726
ok kill yourself retard

[Anonymous No.9806746]

>>9806738
>ok kill yourself retard
You said you looked at the proof and that it's vague, so why don't you post it and point out where you don't follow it?

[Anonymous No.9806749]

>>9806650
>I'm supposed to prove this
What have you tried?

[Anonymous No.9806757]

>>9806668
-Let Q(n) : "P(m) true for all m_0 <= m < n"
-Q(0) vacuously true
-Assume Q(n) true:
Q(n+1): "P(m) true for all m_0 <= m < n+1"
Which leaves P(n) to be proven, but by hypothesis assuming Q(n) true implies that P(n) is true and so Q(n+1) is also true.

So this proves that Q(n) is true for all n, which means that P(m) is true whenever m >= m_0.

Actually I get it now

[Anonymous No.9806765]

>>9806749
>>9806746
Ok so folks now:
Let n be a natural number, and let P(m) be a property pertaining to natural numbers such that whenever P(m+1) is true, then P(m) is also true. Suppose that also P(n) is true. Prove that ∀(m≤n) P(m). Hint: induction on n.

Attempt at proof:
-Let Q(n) : "P(m) true for all m <= n"
-Q(0) true because m <= 0 implies m = 0 = n and P(n) true by hypothesis.
-Assume Q(n) true:
-With Q(n+1) by hypothesis P(n+1) is true (right?) and thus P(n) is true. We need to prove that P(m) is true for all m <= n+1. QED bois?

[Anonymous No.9806780]

>>9800402
Okay, say you get punched in the head and black out for a few seconds. Everything's purple, there's no sound, and you can't see the fight anymore. But when you come to expecting to be laid out, your body is actually still standing and doing what you were telling it to do while you were blind and everything was purple.
What the fuck part of your brain did that? Can't be the frontal lobe or whatever part is conscious, right?

[Anonymous No.9806793]

Folks, another question. Typically 0^0 is said to be undefined yet in Tao's analysis Vol 1 we define 0^0 := 1. Are there any important consequences of this? Why does Tao do this? If there are no downsides, why hasn't everyone adopted this definition?

[Anonymous No.9806883]

This is a vague question, but does anyone have tips for target studying? So far, I've just been looking at each question and summarizing the information I would need to answer it.
My university publishes past exams from all of their courses. For an upcoming exam, there are 5 previous papers available, and of the ~25 total different questions across all past exams, all of them seem to show up multiple times. The exam offers a selection of 12 questions of which we have to answer 6. Subject is paleontology + sedimentology if it matters.

[Anonymous No.9807136]

why dont we just have one giant tooth for each gum that stretches the whole way back?

[Anonymous No.9807141]

>>9807136
Your single tooth won't be able to keep up with your jaw growth. There'd probably be some negative evolutionary selection for that tooth system as well, get an infection/caries - lose the entire arch

[Anonymous No.9807147]

>>9807141
what if one tooth, but like a shark.

[Anonymous No.9807150]

is there any evolutionary advantage to having a sense of humor?

[Anonymous No.9807158]

>>9807136
delete that damn picture

[Anonymous No.9807165]

>>9800697
i dont know but have you considered going on a photography adventure and making your own?

[Anonymous No.9807203]

>>9807141
thank you science

[Anonymous No.9807484]

have i gone off the deep end /sci/? i believe that whites are displaced because we have a surplus of talent, not a shortage of talent. whites tend to pursue left-wing endeavors in their spare time. open source software and ground-breaking public research. this is the final answer i've come up with to all this nonsense. this propaganda. all of it is to keep talent and sanity separate from left-leaning institutions and politics. things were so different 10-15 years ago. i don't know how many people can understand this. am i an insane bigot? have i really lost my mind to depression and madness?

[Anonymous No.9807489]

i really can't tell why things are the way they are. it's so confusing, but i sense something's wrong.

[Anonymous No.9807499]

these feelings of unease and these phenomena cannot be adequately explained by "politically correct" theories. so i must use theories that are not politically correct.

[Anonymous No.9807505]

>>9807484
>>9807489
>>9807499
Go read a book

[Anonymous No.9807506]

>>9807505

you're not answering my questions. i'm serious. this is serious.

[Anonymous No.9807607]

Need help with making a math formula for which game I should play first.
Got a list of video games I want to play, each title ranked by filesize in GB, price and how much I want to play it on a scale from 1-5, 5 being the most.

The smaller GB and price is the better.

[Anonymous No.9807794]

What is the proof (or name of the theorem) that says every nth root is either integer or irrational for natural numers?
why are there no rational roots for natural numbers?

[Anonymous No.9807799]

>>9807794
Because if it was rational you could split it into root of the numerator and denominator

[Anonymous No.9807811]

>>9807794
>why are there no rational roots for natural numbers?
there are, for example sqrt(4)=2

[Anonymous No.9807887]

>>9807799
>>9807811
Thank you but what I really mean is why no natural number (or positive integer) has a root of the form a/b where "a" and "b" are also natural numbers and "a" is not a multiple of "b". Why do natural number roots have to be irrational if they are not integers?

[Anonymous No.9807913]

>>9807887
assume a^(1/n) = b/c.
then a= b^n/c^n, so c^n divides b^n, so c divides b^n.
any prime dividing c also divides b^n, and any prime dividing b^n also divides b, so any prime dividing c also divides b, so c divides b

[Anonymous No.9807934]

>>9800402
Hey guys, I'm trying to code a needle and I made the tip for it, but I don't know how to make the bottom end of the needle

Here is the code, my next post will show how it looks rn

Im a coding/matlab noob, so really appreciate any guidance or resources to look at too

[Anonymous No.9807941]

>>9807934
The figure's bottom rn extends infinitely

I want to cut it off so it's geometry is like that of an actual needle. I suppose I would use a plane to cut it

Thanks in advance guys!

[Anonymous No.9807986]

>>9807484
>whites are displaced because we have a surplus of talent
White *JEWS* are displaced and have a surplus of talent. Just look at all the Nobel Prize recipients. Whites are smarter than blacks and latinos, yes, but they're not too smart for their own good.

[Anonymous No.9808008]

sodium hydroxide NaOH and iron(II) acetate Fe(CH3COO)2 are mixed. Write the formula of any precipitate that could form.
I'm going through a homework and have gotten everything right but this. I think I am missing a step to balance the equation or something.

[Anonymous No.9808157]

at what class am I considered to be actually doing "college level math(s)"?

[Anonymous No.9808158]

>>9808157
>at what class am I considered to be actually doing "college level math(s)"?
any class offered by a college

[Anonymous No.9808161]

>>9808158
yeah but I started with the college equivalent of high school algebra 1 in fall 2017, and I'm starting calc 1 in fall 2018

so what's the deal

[Anonymous No.9808181]

>>9808161
Calc 1 is the first college math course for most STEM normies. /sci/ of course will say that you have to finish Calc 3 and DE before you're really doing "college" math - since high-schoolers are now given opportunities to take those before college.

>>9808008
Are sodium acetate and iron hydroxide valid products? I vaguely remember that acetate or carbonate or whatever can break down into soluble components. I know that's not helpful. It's been a while.

[Anonymous No.9808217]

Is fire a form of plasma?

[Anonymous No.9808248]

>>9808217
No. However, incredibly hot (i.e. thousands of degrees) fire may have plasma in it. Usually the matter "behind" fire is made of gas, but fire itself is the heat/light byproduct of an exothermic reaction. Fire isn't plasma; you could argue that it isn't gas either, and in fact doesn't have a matter state because it is not made of matter at all.

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

[Anonymous No.9808262]

>>9808248
Kinda figured that was the case

[Anonymous No.9808300]

How do you learn "faster", likewise comprehending material and stuff than you would normally? Any advice?

[Anonymous No.9808493]

How do I calculate the molar heat of a reaction given stuff like [math]\Delta t[/math] and mass?

[Anonymous No.9809460]

I can't find a proof anywhere for dis

[Anonymous No.9809472]

>>9809460
that's a definition, there's no need for a proof

[Anonymous No.9809480]

how do I know what "a suitable choice for x" is

[Anonymous No.9809494]

>>9809480
I figured it out.
set x to the roots of the rational expression.

[Anonymous No.9809553]

HELP ME! FUNCTIONAL ANALYSIS GENIUSES, I NEED YOU RIGHT NOW!

Suppose that [math]\|T(f)\|\leq C\|f\|[/math] for all real-valued trigonometric polynomials, for some bounded linear operator [math]T[/math].

I now need this to be true for all complex-valued trigopolys. We can write [math]f=P+iQ[/math], where [math]P[/math] and [math]Q[/math] are real-valued trigopolys. All I get is

[math]\|T(f)\|=\|T(P)+iT(Q)\|\leq C\|P\|+C\|Q\|[/math].

But how can I estimate this by [math]2C\|f\|[/math]? Am I really such a brainlet?

[Anonymous No.9809560]

>>9809553
Wow, 1 sec after posting I found out how. By one simple complex analysis estimate we have |P|,|Q|<=|f|... The norm is Lp([0,2pi)) for p>=1, so by easy reasoning this holds for the norm too. I am such a brainlet.

[Anonymous No.9809607]

what the fuck am I doing wrong, the left hand side keeps adding up to -6 A, whereas the right hand side is -30 A. The back of the book says the answer is -30 A, but I don't know how I'm fucking up the line integral here.

[Anonymous No.9809617]

>>9809607
I should specify, it's L2 that I'm positive I keep fucking up, because the sum of the paths I get is 0+12-15-3= -6, if it was -12 A for path 2, it would add up to -30 A.

[Anonymous No.9809742]

Can one of you explain to me why internal bleeding, in the abdomen, causes pain?

I had it a few months ago and it was painful as shit, throbbing pains, but there was no damage to my abdomen/organs?

[Anonymous No.9809832]

>>9809472
Why is it defined that way?

[Anonymous No.9809845]

>>9809832
why is anything defined the way it is?

[Anonymous No.9809848]

>>9800654
you won the brainltet of the yeaar

[Anonymous No.9809851]

it took me 6 months to discover how to calculate the red funtion with the other 3. It was untill i coursed linear algebra

[Anonymous No.9809865]

>>9809851
>mexican intellectuals

[Anonymous No.9809869]

>>9809865
argentinian. Bro I was only 18

[Anonymous No.9809875]

>>9809865
the worst thing is i asked a public highschool maths teacher and he was mindblown. What a retard

[Anonymous No.9809923]

Right, so I have no fucking clue which board to put this on but I guess it’s biology related so fuck it whatever

Basically I was a fucking dumbass and fucked myself too hard with my new dildo and now I’m bleeding and getting cramps like I brought on my period. I’m on birth control and still have about 2 weeks before my scheduled real period. What the fuck happened? Did I tear the shit out of my vagina or something? I feel like a fucking dumbass because it’s embarrassing as hell and I don’t really want to have to go to my OBGYN if it’s benign so now I’m just sitting in my anxiety wondering when I’ll go back to normal.
Sorry for bothering you, /sci/.

[Anonymous No.9809939]

>>9809923
go see a gynecologist you fucking degenerate
getting health advice from the internet is retarded already, but consulting a website full of male trolls for vagina problems is peak brainlet

[Anonymous No.9810221]

>>9809939
Thanks anon, just spaghetting over here. I’ll talk to someone.

[Anonymous No.9810772]

How did you guys learn physics in the beginning?

Did you just read textbooks and do the problems? I'm getting annoyed because it feels like I have to memorize so many equations. I feel like it's probably possible to derive these equations if you're not a brainlet and they would just come to you intuitively.

[Anonymous No.9810824]

Is density in elements perfectly correlated with weight? The denser the element, the heavier it is, it's that simple?

[Anonymous No.9810825]

>>9810772
the textbook should have the derivation for the equations in it. if it doesn't, get another one.
you can always just memorize the derivations from the underlying axioms, but at some point it will be too time intensive to not memorize specific equations.

[Anonymous No.9810827]

>>9810824
that's how it's defined

[Anonymous No.9811119]

is it possible to squeeze memories into a nanosecond and recall every moment of it?

[Anonymous No.9811601]

>>9809832
It's defined that way because the quantity
[eqn]
\sum_i a_i b_i
[/eqn]
transforms as a scalar.

[Anonymous No.9812049]

>>9800402
Would the heat dissipated from a radiator on a cooling device, say any given wall mounted ac unit, be able to heat water to it's boiling point?

I imagine a radiator on a car could as them shits will evaporate water on the surface, but could that same effect be achieved through electric power?

[Anonymous No.9812056]

>>9800654
>can single celled organism get a disease where malfunctioning cells disrupt organic functions
no

[Anonymous No.9812058]

Why is 6 afraid of 7?

[Anonymous No.9812087]

>>9800655
If the average kinetic energy is K and there are n molecules then clearly n-1 having 0 energy and the last one having n*K averages to K and there is no way to do better than that.

[Anonymous No.9812090]

>>9812049
Evaporation happens without molecules reaching their boiling point.

[Anonymous No.9812108]

>>9800402
Why does [math]\sum^\infty_{i=1} \frac{9}{10}(\frac{1}{10})^n[/math] converge to [math]\frac{\frac{9}{10}}{1 - \frac{1}{10}}[/math]? Am I a brainlet?

[Anonymous No.9812204]

I'm working through an undergrad linear algebra textbook, and I'm stuck on a problem that asks whether the set of all symmetric n x n matrices are a vector space. I think it is, because it's closed under vector addition and scalar multiplication, but I'm not certain.

[Anonymous No.9812282]

>>9812049
> Would the heat dissipated from a radiator on a cooling device, say any given wall mounted ac unit, be able to heat water to it's boiling point?
Yes. You'd just need to increase the compression ratio. An A/C or refrigerator only needs to raise the temperature to above that of the atmosphere in order to lose heat. Beyond that, a larger radiator is preferable to a higher temperature.

> but could that same effect be achieved through electric power?
There are lots of electric heating devices which run at or above 100C.

[Anonymous No.9812284]

>>9812108
Note that (9/10)/(1-1/10) = (9/10)/(9/10) = 1.

[Anonymous No.9812308]

>>9812284
But how was [math]\frac{a}{1-r}[/math] derived

[Anonymous No.9812352]

>>9812108
that's wrong
[eqn] \sum_{i=1}^{\infty} (\frac{1}{x})^i =\frac{1}{x}+\sum_{i=2}^{\infty} (\frac{1}{x})^i \\\
\qquad \quad ~=\frac{1}{x}+\sum_{i=1}^{\infty} (\frac{1}{x})^{i+1} \\\
\qquad \quad ~=\frac{1}{x}+\frac{1}{x}\sum_{i=1}^{\infty} (\frac{1}{x})^i \\\
\sum_{i=1}^{\infty} (\frac{1}{x})^i =s=\frac{1+s}{x} =\frac{1}{x-1} [/eqn]
use 10 for x and multiply by 9/10 to get 1/10
https://www.wolframalpha.com/input/?i=sum+of+(9%2F10)*(1%2F10)%5En+from+1+to+infinity

[Anonymous No.9812365]

Brainlet here:

Can someone give me a quick rundown on radio waves and how they travel?

[Anonymous No.9812380]

>>9812204
Yes, for the reasons you give.

[Anonymous No.9812511]

Is there a possibility that black holes don't have singularities because from the perspective of anything inside, they fall past the event horizon then end up eons in the future when the black hole dies?

[Anonymous No.9812512]

If I spend a large portion of my day on /sci/, on mos days, can I still think of myself as being smart?

[Anonymous No.9812575]

What the FUCK is this

[Anonymous No.9812578]

>>9812575
How's highschool?
Look up the lensmaker equation. o is the object, f is the focal point of the lens, and I is the image. The top depicts a concave lens, while the bottom is a convex mirror.

[Anonymous No.9812702]

This is a birthday problem question: "Suppose we divide a population of 1,000,000 people randomly into groups of 3. How many groups can we expect there to be in which all persons share the same birthday?"
if we let X be the number of groups with everyone having the same birthday, would X be distributed:
X~Hyp(n=3, r=333333, N=1000000)
or would it be distributed binomially with 3 trials and with probability of each trial equal to 365/365^(333333) so
X~Bin(n=3, p=365/365^(333333)?

[Anonymous No.9812708]

Where around the house can I find metals with low melting points?
Like tin, lead, or zinc?

[Anonymous No.9812714]

Hi, would someone care to explain how the highlighted answer is incorrect

[Anonymous No.9812716]

Shouldn't the homogenous solution be Ae^6x + Be^-2x?

[Anonymous No.9812733]

>>9812708
Also is the outside parts of Lithium coin batteries made of pure Lithium metal?

[Anonymous No.9812738]

>>9812716
Are any of these solutions even correct??

[Anonymous No.9812749]

>>9812716
Clearly that’s not a solution, since if you plug it in the left hand side would just a combination of exponential functions

[Anonymous No.9812756]

>>9812749
The homogenous equation will have characteristic equation (m-6)(m+2)=0 so y_h(x)=Ae^6x+Be^-2x

[Anonymous No.9813490]

I graduated from high school and calculus class but I don't even know what a polynomial is

Should I be alarmed?

[Anonymous No.9813509]

>>9812702
The probability that a group of 3 contains no birthdays which are the same (assuming 365 days a year) is 365*364*363/365^3. We want the complement so (1-that)*10^6

[Anonymous No.9813549]

Why does Bragg diffraction related to lattice planes?
It's individual atoms that cause the scatter and why should a wave be scattered exactly at the same angle as the incoming one?

[brainlet No.9813586]

https://proofwiki.org/wiki/Leibniz%27s_Formula_for_Pi/Leibniz%27s_Proof
So in the proof for Leibniz's formula, I don't understand how he gets the result y^2/1 + y^2 = y^2 - y^4 +y^6 - y^8 +... from Sum of Geometric Progression, probably because the initial equation (y^2/1 + y^2) seems to be a different form from the equation in Sum of Geometric Progression (x^n - 1/ x - 1). Can you help a brainlet out

[Anonymous No.9813643]

>>9813549
Fairly good question.
The picture you have there is a (semi)classical one, and it obviously works as confirmed by experiments. You can look up the Laue equations for a more rigorous treatment, and Bragg's condition arises somewhat naturally from those.

[Anonymous No.9813681]

Is gravity just electromagnetism?

[Anonymous No.9813686]

>>9813681
Yes, it certainly isn't "curvature of space-time".

[Anonymous No.9813688]

>>9813681
No.

[Anonymous No.9813750]

Does anybody know of any experiments to study the effects of slowed/hastened development through chemical means on the mental capacity of animals?

[Anonymous No.9813759]

>>9813681
The really interesting thing here is that magnetic objects dont have a gravitational field. It might suggest something like this when I think about it.

[Anonymous No.9813807]

>>9813759
they do no work and therefore have no energy. they're also a shadow of the electric field from a different velocity

[Anonymous No.9813814]

>>9800402
How to solve higher order ODE using undetermined coefficients? I keep getting stuck when I plug the derivatives back into the problem to solve for thr coefficients

[Anonymous No.9813838]

>>9813586
Guys seriously my inability to understand this is actually making me nauseous

[Anonymous No.9813863]

>>9813838
geometric progression formula for r<1:

[eqn]\frac1{1-r}=\sum_{k=0}^\infty r^k[/eqn]

now just take r = -y^2 and multiply the whole expression by y^2

[Anonymous No.9813865]

So i just finished watching a talk about the higs field and quantum field theory in general and by the end of it I was perplexed that here is this guy watering down stuff for the masses to understand and the questions that were addressed to him in the Q&A session were nothing short of inappropriate if not moronic.
So it got me thinking,are people deliberately this dense?
I am not physicist but the talk made sense in every aspect.
Why are people doing this?

[Anonymous No.9813977]

What are all the ways or at least the comnon ways to determine if a number is a perfect square or not?

[Anonymous No.9814235]

>>9813977
Check whether its square root is an integer.

[Anonymous No.9814250]

Hi,
Is the homogenous solution to y''-4y'-12y=0
y=exp(6x)(Acos(2x)+Bsin(2x))? Can you prove/disprove it?

[Anonymous No.9814294]

can you combine a microwave gun and a flamethrower to make a plasma gun

[Anonymous No.9814317]

The BFGS update for the hessian is
in the top equation in pic.
How you get to the second equation? H is the inverse of B. I know you're supposed to use the Sherman-Morrison-Woodbury formula but I can't seem to correctly derive the second equation

[Anonymous No.9814344]

>>9814250
>Is the homogenous solution to y''-4y'-12y=0
>y=exp(6x)(Acos(2x)+Bsin(2x))?
Why would it be?

[Anonymous No.9814428]

>>9814250
No. The characteristic polynomial is s^2-4s-12=(s-6)*(s+2) which has two real roots: s=6,s=-2. So there's no sin/cos terms. It's: Ae^6x+Be^-2x.

[Anonymous No.9814448]

>>9813549
It's from Heisenberg uncertainty.
Incoming wave has well defined momentum so there's a uncertainty in position.
Now when it enters the solid this uncertainty gets scattered at a lattice plane.

[Anonymous No.9814536]

So one of the properties of e is that integral from e to 1 for function (1/x) is equal to 1.

Where is this property used?

[Anonymous No.9814617]

What metal could this little Eiffel Tower statuette be made of?

It had a small amount of patina at the bottom corners until today when I.washed it it became green all over. Normally it had a dull bronzy type of colour.

[Anonymous No.9814644]

>>9814617
brass maybe

[Anonymous No.9814647]

Let the three right lines PT, TQV, VR touch the figure described in as many points, P, Q, R, and meet in T and V. On the tangents erect the perpendiculars PA, QB, RC, reciprocally proportional to the velocities of the body in the points P, Q, R, from which the perpendiculars were raised; that is, so that PA may be to QB as the velocity in Q, to the velocity in P, and QB to RC as the velocity in R to the velocity in Q. Through the ends A, B, C, of the perpendiculars draw AD, DBE, EC, at right angles, meeting in D and E: and the right lines TD, VE produced, will meet in S, the centre required.
is AD parallel to PT, and CE parallel to RV, or are AD or CE parallel with each other. The language isn't quite clear. From Newton's Principia proposition 5 problem 1, pic related

[Anonymous No.9814651]

>>9814617
It looks like a copper alloy to me, try cutting it a little and observe the colour where you cut it, should be copperish, also test if it's magnetic

[Anonymous No.9814652]

Is IQ of 115-125 enough to strive for Masters in engineering? Not that I know it yet, I got lime 37 in 45 FRT test

[Anonymous No.9814657]

>>9814651
Non-magnetic. Scratching at it there's a light golden colour underneath the green patina. Strangely though there is silver underneath if I scratch deeper and damage the metal. So I suspect it's bass plated aluminum? But I'm new to metals so I wouldn't be certain.

[Anonymous No.9814718]

>>9814617
I got this exact same thing but one leg is broken.

[Anonymous No.9814840]

I had some rain this morning and I saw what looked like a crease in the clouds. Two cloud formations side by side had a distinct darker line going through them, and that crease or fold stretched for about 70 degrees. there was a bit of wind but nothing too severe. what would cause such a thing? attached is a very shitty artist rendering of what I saw

[Anonymous No.9814993]

>>9813977
if its prime factorisation only has even exponents

[Anonymous No.9815009]

>>9812714
well for one, answers 2 and 3 are the same

[Anonymous No.9815050]

>>9814536
Nvm found it. Natural logarhitm of any number >= 1 can be counted my making it the upper limit of that integral.

[Anonymous No.9815132]

>>9800402
I’m having a lot of trouble gaining intuition and understanding about differential equations and the things I’m learning to apply in class. I’ve always been a brainlet when it comes to reading the book. Can anyone recommend any good video series or reads that will deliver conceptual information to me ? Will this stuff come more naturally While I’m taking physics and other applied major coursework?

[Anonymous No.9815173]

>>9813977
Calculate its logarithm to some base b > 1, divide by 2, then raise b to the power of the number that you got, and check whether you end up with an integer.

[Anonymous No.9815403]

how do animals know not to walk off high ledges

[Anonymous No.9815438]

>read an article about the Large telescope array in Chile recently
>article mentions how if all the scopes get used in their array configuration then they're so precise you could spot an astronaut on the moon

uhhhhhh so why don't they just do that, point the business at the moon and show us the landing sites to end the fucking controversy over the landings once and for all?

[Anonymous No.9815556]

>>9809832
https://www.youtube.com/watch?v=LyGKycYT2v0&list=PLZHQObOWTQDPD3MizzM2xVFitgF8hE_ab&index=10

[Anonymous No.9815558]

Aren't atoms technically violating the laws of thermodynamics?

[Anonymous No.9815620]

>>9815558
expand?

[Anonymous No.9815656]

>>9815438
the smallest diameter telescope that could distinguish an object with a diameter of 2 meters a distance of 384,400 km away with light with a wavelength of at least 400 nm given by the rayleigh criterion is given by the following equation
[eqn] D = 1.22 \cdot \frac{\lambda}{\theta} \\\
\theta = \frac{2 ~ \textrm{m}}{384,400 ~ \textrm{km}} \approx 5.203 \cdot 10^{-9} ~ \textrm{rad} \\\
D \approx 1.22 \cdot \frac{400 \cdot 10^{-9} ~ \textrm{m}}{5.203 \cdot 10^{-9}} \\\
D \approx 93.7936 ~ \textrm{m} [/eqn]
The diameter of the ELT is only going to be 39.3 m, so no you could not see an astronaut on the moon with it, even if there was a 100 m diameter telescope it would only be able to just make out the landing sight, as in the picture would be incredibly blurry and lack any necessary detail to distinguish the lander from a rock. This is also ignoring atmospheric effects which would definitely complicate things

The ELT is not even up yet pic related, and first light is supposedly going to be in 2024.

[Anonymous No.9815893]

>>9802105
If i'm measuring earth's gravity at it's core, should i consider the entire earth's mass or only the mass of it's core?

[Anonymous No.9816149]

what's the most effective way to use toilet paper? I usually take 6 pieces at a time, fold it so that's its a doubly thick 3 pieces, and then wipe

[Anonymous No.9816158]

>>9815438
You think that would convince anyone?

[no banter pls No.9816174]

Two questions:

Why is it enough to show it when s=0? Because we could consider the series (sn-s) and apply the same reasoning ?


Why is the first term less than ε and why is the second one less than εr^(M+1)?

[Anonymous No.9816317]

Can a small exposure from a degreaser with a PH of 13-14 cause burns to the hand?

[Anonymous No.9816393]

Dear phenotypes and brainlets, a new thread just launched:

>>9816387
>>9816387
>>9816387

[Anonymous No.9816398]

>>9800654
can amoeba get depression?