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# /sci/ - Science & Math

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No.9263958 [Reply] [Original] [archived.moe]

the other thread >>9256335 is pretty much dead

in the definition of an ideal I of a ring R is there any difference in requiring that I is a subgroup of R under addition and requiring that I is a subring of R?

 >> Anonymous Sun Oct 29 16:31:33 2017 No.9263974 >>9263958yes beacuse not all additive subgroups are subringsby the subring test a subset is a subring if it is closed under multiplication, subtraction and contains the multiplicative identityhttps://en.wikipedia.org/wiki/Subring#Subring_testconsider the ring Z and the subset 2Z which is closed under multiplication and subtraction but doesn't contain the mult. identity 1
 >> Anonymous Sun Oct 29 16:34:25 2017 No.9263978 How is the big crunch not the correct conclusion for the end of universe?
 >> Anonymous Sun Oct 29 16:44:30 2017 No.9264006 >>9263958I'm just not understanding feynman's method of integrating bounded integrals of two functions. In the explanation, they appear to use a kernel, something of a 'b' thrown into an integral to equate it to a partial derivative within the integral. I just don't get how you choose WHERE to throw the 'b' in. A very popular example is the integration of\int_{0}^{\pi} $e^{\cos{x}}*{\cos{\sin{x}}}*dx$ into \int_{0}^{\pi} $e^{b*\cos{x}}*{\cos{b*\sin{x}}}*dx$ >HOW DID THEY CHOOSE WHERE TO PUT THE b
 >> Anonymous Sun Oct 29 16:46:24 2017 No.9264010 >>9264006also, not very good with LaTeX$\int_{0}^{\pi} [math]e^{\cos{x}}*{\cos{\sin{x}}}*dx$[/math] into \int_{0}^{\pi} $e^{\cos{x}}*{\cos{\sin{x}}}*dx$[/math]
 >> Anonymous Sun Oct 29 17:22:54 2017 No.9264088 Where can I find people that will help me with my homework without making fun of me or telling me to fuck off?
 >> Anonymous Sun Oct 29 17:28:05 2017 No.9264097 >>9264088I'm sure someone will do that in exchange for money
 >> Anonymous Sun Oct 29 17:57:26 2017 No.9264158 >>9264006wtf? do you mean [eqn]\int_0^\pi e^{\cos x}\cdot\cos\sin x\,dx[/eqn]into [eqn]\int_0^\pi e^{b\cos x}\cdot\cos (b\sin x)\,dx[/eqn]?I can't answer the question, but please read the sticky and learn the formattingbasics so someone who might can understand it: start with a [ math] or [ eqn] tag and end with a [ /math] or [ eqn] tag, respectively (without the spaces obviously), don't use dollar $igns, place parentheses around non-trivial function arguments and use \cdot for a multiplication dot  >> Anonymous Sun Oct 29 17:59:07 2017 No.9264161 >>9263958How do I construct the green's function from this form?$\mathcal{L}\{G(t,\tau;\vec{x},\vec{\xi})\} = \delta(t-\tau,\vec{x}-\vec{\xi})$ Say for example L is the heat equation's operator  >> Anonymous Sun Oct 29 18:00:09 2017 No.9264166 >>9264161$\mathcal{L}\{G(t,\tau;\vec{x},\vec{\xi})\} = \delta(t-\tau,\vec{x}-\vec{\xi})$  >> Anonymous Sun Oct 29 18:14:00 2017 No.9264189 >>9263958>in the definition of an ideal I of a ring R is there any difference in requiring that I is a subgroup of R under addition and requiring that I is a subring of R?Yes, An ideal is a subring with the additional property that any element OUTSIDE of the ideal multiplied by any element of the ideal is INSIDE the ideal.That property is there so that the quotient can be made into a ring by defining this multiplication (a+I)(b+I):=ab+I.For it to be well defined, it has to be independent of the representatives, and for this to happen you need the additional property.  >> Anonymous Sun Oct 29 18:15:02 2017 No.9264190 >>9264088fuck off  >> Anonymous Sun Oct 29 18:23:14 2017 No.9264200 File: 20 KB, 631x261, aa7.png [View same] [iqdb] [saucenao] [google] >>9263974>>9264189thanks. so the definitions in pic related arent equivalent?  >> Anonymous Sun Oct 29 18:52:49 2017 No.9264255 >>9264200The second definition is a bad one.  >> Anonymous Sun Oct 29 19:15:38 2017 No.9264306 >>9264200They are equivalent.The first one at (ii) acounts that multiplication in I is closed (thus subring), and that for x outside I and y in I you have xy in I and yx in I (ideal subring).The second one is a retarded definition. It's correct, but redundant.Change textbook. This one seems bad.  >> Anonymous Sun Oct 29 19:17:17 2017 No.9264310 >>9264306>They are equivalent.They're not. Since I is a subring in the second definition, it contains 1, and so R itself would be the only ideal because of (I2).  >> Anonymous Sun Oct 29 19:19:28 2017 No.9264316 Did 0! = 1 first come from definition or from the Gamma Function? I'm assuming the former but heard someone imply it was the latter. Curious.  >> Anonymous Sun Oct 29 19:27:18 2017 No.9264329 >>9264306>The first one at (ii) acounts that multiplication in I is closed (thus subring)Wrong,  >> Anonymous Sun Oct 29 19:43:31 2017 No.9264355 File: 1.25 MB, 857x2352, hags_theorem.png [View same] [iqdb] [saucenao] [google] >>9264161First let us look at the symmetries of $\mathcal{L}$. Suppose $T_\vec{a}$ and $T_\beta$ are representations of the space and time translation operators such that $(T_\vec{a}f)(\vec{x},t) = f(\vec{x} - \vec{a},t)$ and $(T_\beta f)(\vec{x},t) = f(\vec{x},t-\beta)$. If $[T_\vec{a},\mathcal{L}] = [T_\beta,\mathcal{L}] = 0$ then it follows that $G$ is also translationally invariant, and therefore $G(\vec{x},\vec{\xi},t,\tau) = G(\vec{x}-\vec{\xi},t-\tau)$. So you can WLOG solve the PDE $\mathcal{L}G(\vec{x},t) = \delta(\vec{x},t)$ to get the Green function, namely the Green function at the origin and $\tau=0$ determines the full Green function.If the above is satisfied then you can perform a Fourier transformation. Given $G \in \mathcal{S}(\mathbb{R}^n)$ is a Riemann square-integrable distribution in space (i.e. $G\rightarrow 0$ as $\vec{x} \rightarrow \pm \infty$), you can Fourier transform in the $\vec{x}$ coordinates and obtain an ODE in $t$ which you can solve depending on initial conditions, then inverse Fourier transform back into real space. If $G\in \mathcal{S}(\mathbb{M})$ is a square-integrable distribution in both the space and time coordinates then you can let $x = (t,\vec{x})$ and Fourier transform in $x$. This gives you an algebraic equation that you can just inverse Fourier transform back directly.  >> Anonymous Sun Oct 29 19:59:56 2017 No.9264371 >>9264310Subrings don't necessarily have a unit. A ring might not necessarily have a unit. And even if the ring and the subring have units, they might not even be equal.>>9264329Are you retarded or what? I is a subset of R.  >> Anonymous Sun Oct 29 20:00:59 2017 No.9264373 >>9264371I meant "unity", not "unit".  >> Anonymous Sun Oct 29 20:02:56 2017 No.9264375 >>9264371>Are you retarded or what? I is a subset of R.Not enough to guarantee being a subring.  >> Anonymous Sun Oct 29 20:03:51 2017 No.9264376 >>9264371>Subrings don't necessarily have a unit.They do for any useful applications.  >> Anonymous Sun Oct 29 20:05:47 2017 No.9264380 >>9264371>A ring might not necessarily have a unitWrong.Those are called rngs.  >> Anonymous Sun Oct 29 20:08:58 2017 No.9264388 >>9264375Wrong.1) It is a subset of R.2) It is a subgroup from the hypothesis.2) Multiplication can be restricted there since I is closed under it.3) Associative and distributive laws for * trivially follow since + and * on S are the same ones as on R, just restricted to S.  >> Anonymous Sun Oct 29 20:09:14 2017 No.9264390 >>9264371>if the ring and the subring have units, they might not even be equal.Also wrong.  >> Anonymous Sun Oct 29 20:10:05 2017 No.9264391 File: 70 KB, 645x729, 1508888817247.png [View same] [iqdb] [saucenao] [google] >>9264376>They do for any useful applications.  >> Anonymous Sun Oct 29 20:11:01 2017 No.9264394 >>9264388>1) It is a subset of R.>2) It is a subgroup from the hypothesis.>2) Multiplication can be restricted there since I is closed under it.>3) Associative and distributive laws for * trivially follow since + and * on S are the same ones as on R, just restricted to S.Still not a subring, existence of a multiplicative identity is not implied by any of these statements.Next?  >> Anonymous Sun Oct 29 20:13:36 2017 No.9264404 >>9264390$\mathbb{Z} \times \mathbb{Z}$ has unity $(1,1)$ .$\mathbb{Z} \times \{0\} \unlhd \mathbb{Z} \times \mathbb{Z}$ has unity $(1,0)$ .  >> Anonymous Sun Oct 29 20:15:29 2017 No.9264408 File: 56 KB, 645x773, 1496829712394.jpg [View same] [iqdb] [saucenao] [google]  >> Anonymous Sun Oct 29 20:15:47 2017 No.9264409 >>9264390>wrong>wrong>wrong>everything turns out to be rightyou're just a retard  >> Anonymous Sun Oct 29 20:17:23 2017 No.9264413 >>9264404>Z×{0}⊴Z×ZWrong. Not a subring, doesn't contain the ring's multiplicative identity.  >> Anonymous Sun Oct 29 20:18:23 2017 No.9264417 >>9264409>you're just a retardNothing I claimed was wrong has turned out to be right.Next?  >> Anonymous Sun Oct 29 20:19:37 2017 No.9264421 >>9264417>hurr I'm right even when I'm wrongNext?  >> Anonymous Sun Oct 29 20:20:23 2017 No.9264422 >>9264408Your personal blog is not a legitimate source.Next?  >> Anonymous Sun Oct 29 20:20:54 2017 No.9264424 >>9264421>Next?Unless you finally point out something I claimed incorrectly (which you can't), there is no "next".  >> Anonymous Sun Oct 29 20:22:31 2017 No.9264426 >>9264413>>9264422I bet you are the same retard who spams Wildberger memes.  >> Anonymous Sun Oct 29 20:23:45 2017 No.9264430 >>9264426>I bet you are the same retard who spams Wildberger memes.You lost that bet.Plus that doesn't even make any sense, you're the one using unconventional naming and just generally being confused about mathematical standards.  >> Anonymous Sun Oct 29 20:34:11 2017 No.9264454 >>9264430>unconventional namingIt's not unconventional at all. It's what most texts use.If you define a ring to have unity, then you'd get shit like "the kernel of a homomorphism is not necessarily a subring" which is plain fucking retarded.It's just bad terminology. There is no reason to restrict the definition.  >> Anonymous Sun Oct 29 20:35:34 2017 No.9264457 >>9264454>It's not unconventional at all.Wrong.>It's what most texts use.Wrong.>[blah blah] which is plain fucking retarded.How so?  >> Anonymous Sun Oct 29 20:37:13 2017 No.9264458 File: 14 KB, 200x226, e09.png [View same] [iqdb] [saucenao] [google] >>9264457whatever you say, friend  >> Anonymous Sun Oct 29 20:38:15 2017 No.9264462 >>9264458Feel free to attempt to lend credence to any of your inane statements.  >> Anonymous Sun Oct 29 20:39:25 2017 No.9264465 >>9264462>lend credence>inane You seem very smart, since you are using such words.I concede.  >> Anonymous Sun Oct 29 20:41:16 2017 No.9264467 >>9264465>You seem very smartI'm not, just smarter than you.  >> Anonymous Sun Oct 29 20:42:31 2017 No.9264469 >>9264467true  >> Anonymous Sun Oct 29 20:46:48 2017 No.9264478 >>9264376Meh, there are some relatively natural examples of rings that don't have units (for example L^1 with convolution)  >> Anonymous Sun Oct 29 20:48:20 2017 No.9264484 >>9264478>natural examples of rings that don't have units (for example L^1 with convolution)That isn't a ring, it's a rng.  >> Anonymous Sun Oct 29 20:56:06 2017 No.9264503 Can someone tell me why this regular expression is failing to accept?regex: [0-9]{5}input: 12345  >> Anonymous Sun Oct 29 21:31:57 2017 No.9264593 >>9264088Has no one ever heard of tutoring before? Or is /sci/ too socially retarded that the aspect of getting help in person deters them?  >> Anonymous Sun Oct 29 21:44:25 2017 No.9264616 >>9264593The latter, and that you usually have to pay for tutors.  >> Anonymous Sun Oct 29 22:01:08 2017 No.9264665 >>9263958Why does gas cause feelings of depression and anxiety? It's a pretty immediate effect in most people but I can't find out why.  >> Anonymous Sun Oct 29 22:19:00 2017 No.9264703 >>9264355Thanks anon.  >> Anonymous Sun Oct 29 22:28:40 2017 No.9264722 >>9263978Because it looks like space itself is expanding at a rate so fast that the effects of gravity will be to weak and slow to pull all the mass back together. It's looking like a big rip or heat death.  >> Anonymous Sun Oct 29 22:29:27 2017 No.9264723 Not exactly a science question but more of a person question.How do I find purpose in life when I'm an atheist?  >> Anonymous Sun Oct 29 22:29:43 2017 No.9264724 >>9264088Your uni probably has tutors and shit yo.  >> Anonymous Sun Oct 29 22:32:51 2017 No.9264730 >>9264723As a fellow athiest I ran into this as well. Your purpose is whatever you want it to be. You just need to focus on doing whatever you focus on well, and being happy.  >> Anonymous Sun Oct 29 22:55:38 2017 No.9264775 >>9264730What if I focused on becoming a serial killer and started murdering people at random and did it because I wanted to? People like you make atheists look retarded. Really smart right there.  >> Anonymous Sun Oct 29 23:15:23 2017 No.9264815 >>9264775>make atheists look retardedIt's not hard.  >> Anonymous Sun Oct 29 23:23:54 2017 No.9264825 Pic is shopped?  >> Anonymous Sun Oct 29 23:26:50 2017 No.9264829 >>9264775>Taking something to the most extreme, unlikely conclusion because you didn't like my answerOk buddy. Just be sad and depressed then.>What is my purposeTo kill yourself  >> Anonymous Sun Oct 29 23:32:02 2017 No.9264835 >tfw i get legitimately blindingly enraged when I get stuck on a problem for too long  >> Anonymous Sun Oct 29 23:35:48 2017 No.9264839 Why isn't the earth perfectly flat? Shouldn't the north pole sag down to make it flat? Like with tectonic plates  >> Anonymous Sun Oct 29 23:36:16 2017 No.9264840 File: 51 KB, 200x200, 1501018980644.png [View same] [iqdb] [saucenao] [google] >>9264825No.  >> Anonymous Mon Oct 30 00:10:51 2017 No.9264883 >>9264839>Shouldn't the north pole sag down to make it flat?Why would it? Gravity pulls toward the center of the earth.  >> Anonymous Mon Oct 30 00:14:32 2017 No.9264888 >>9263958Is EE really as bad as its famed to be? I find the topic incredibly fascinating but I question whether I'm intelligent enough to make it. I was thinking of going to college this next semester, but I'm worried about being overwhelmed. I have a very poor math education and a lot of catching up to do.Does anyone have any textbooks or resources you'd recommend so I can get an idea of what I'm in for?  >> Anonymous Mon Oct 30 00:17:49 2017 No.9264894 >>9264840Wait.... so big head ed is not a meme?  >> Anonymous Mon Oct 30 00:20:02 2017 No.9264903 >>9264883So gravity pulling the sides is why it's pushed up to make the dome on top?Like a carpet?  >> Anonymous Mon Oct 30 00:22:18 2017 No.9264908 File: 24 KB, 400x382, 1500484867942.jpg [View same] [iqdb] [saucenao] [google] >>9264894No. I attended one of his conferences on paracompactification of the moduli space of connections for $N = 2$ superconformalsymmetric string theory and his head was so big that I wasn't able to take down any notes at all.  >> Anonymous Mon Oct 30 00:24:44 2017 No.9264910 >>9264503bumping this. using C# btw  >> Anonymous Mon Oct 30 00:52:19 2017 No.9264958 Hi, https://www.youtube.com/watch?v=ufU6b7OHb8MCan someone quickly derive this formula in this video at 26:05 where he goes from the halves to the 2 minus the exponentials? I know that he's trying to get the real parts of the exponential, and to do so he has to add another exponential of opposite sign. I don't understand why both exponential terms are negative (one must be rotating one way, and the other in the opposite direction)..Besides that, how does he get from the halves to the next part? It's basic integration, I get it, but based on the rules I know so far I can't get it.  >> Anonymous Mon Oct 30 01:48:33 2017 No.9265021 How come sometimes you have to pee really bad, but when you finally do there's a lot less than you expected?  >> Anonymous Mon Oct 30 01:51:56 2017 No.9265025 On Thursday I'm going to take the Mercedes 4Matic exam, what should I expect? Have any of you taken it before?  >> Anonymous Mon Oct 30 01:53:09 2017 No.9265026 >>9265025Fucking autocorrect, I mean the AMATYC exam  >> Anonymous Mon Oct 30 03:03:50 2017 No.9265110 How do i calculate the volume of a unit cell with a two atomic basis ?  >> Anonymous Mon Oct 30 05:21:20 2017 No.9265246 File: 5 KB, 717x29, fxyz.png [View same] [iqdb] [saucenao] [google] Reposting since I posted in the dead thread.I'm supposed to prove $\int \int \int_{E}f(x,y)dxdy$ exists and calculate its value. What I thought I'd do was calculate the integral for the $x^2+y^2\leq z^2+1$ side and substract the integral for the $2z^2\leq x^2+y^2$ side, but since I get $\sqrt{x^2+y^2-1}$ I'm stuck.Does $\int \int \int_{E}f(x,y)dxdy$ actually exist and if so, how should I solve?  >> Anonymous Mon Oct 30 08:37:36 2017 No.9265422 Alright, hoping some cunt will help me. Don't know much about chemistry but am tackling a predictive problem which involves finding the amount of aromatic compounds found in diesel fuels.Why is this useful to be predicting this? In the context of diesel fuels of course.I've done a bit of research and aromatic compounds are apparently especially stable; so maybe you want less of them in your diesel fuels because less aromaticity means less stability; more reactivity - therefore a more energetic combustion?Am I close? Completely wrong? Does it have no real useful effect on diesel fuels and I'm just predicting the aromaticity for the sake of it?  >> Anonymous Mon Oct 30 09:13:59 2017 No.9265451 >>9263958How do I prove that $( f \circ g \circ f)$ bijective is equivalent to $f$ bijective?Would $g$ then also have to be bijective, or can it be anything?  >> Anonymous Mon Oct 30 09:14:13 2017 No.9265453 >>9265422>this level of reddit spacing  >> Anonymous Mon Oct 30 09:22:12 2017 No.9265461 >>9265453I thought it would be a bit more readable this way; feel free to copy it all and remove the line breaks though  >> Anonymous Mon Oct 30 09:40:39 2017 No.9265481 >>9265451Pretty sure g being injective would be enough.  >> Anonymous Mon Oct 30 09:41:47 2017 No.9265483 >>9265481sorry, I meant surjective  >> Anonymous Mon Oct 30 09:44:50 2017 No.9265487 Are MIT calc lectures good enough for a first course in calculus?Should I complement it with Stewart calculus textbook?  >> Anonymous Mon Oct 30 10:11:17 2017 No.9265514 Let $E\subset \mathbb{R}^n$. Prove that for every $\epsilon >0$ we can find a succession of closed $R_{k}\subset \mathbb{R}^n$ such that $E\subset \bigcup_{1}^{\infty}R_{k}, \sum_{1}^{\infty}R_{k}<\epsilon$ iff for every $\epsilon >0$ we can find a succession of open $A_{k}\subset \mathbb{R}^n$ such that $E\subset \bigcup_{1}^{\infty}A_{k}, \sum_{1}^{\infty}v(A_{k})<\epsilon$.If we have an open $A_{k}$ succession like that we only need to close its terms to find the closed $R_{k}$ succession, but can I prove the converse?  >> Anonymous Mon Oct 30 10:13:08 2017 No.9265519 >>9265451take g = 0 for example, then f(g(f(x)) = f(0) for all x, which isn't bijective unless f is only defined on one element  >> Anonymous Mon Oct 30 10:20:04 2017 No.9265533 >>9265487No lecture is ever better than a textbook.  >> Anonymous Mon Oct 30 10:27:28 2017 No.9265543 how do I get rid of ADD, I can't focus longer than 10min at a time studying somethingI did not used to be like this  >> Anonymous Mon Oct 30 12:32:01 2017 No.9265707 File: 1.22 MB, 540x304, Question.gif [View same] [iqdb] [saucenao] [google] >>9263958What is that dual-way arrow thing in mechanics, I always see it when I'm working with restitution and collisions but never know what it actually is. You know the <->, what is it called and what does it do?  >> Anonymous Mon Oct 30 12:33:35 2017 No.9265709 >>9264454but that is true. That's why most people study ideals as modules. This is by far the approach which is generalized the most (sheaf of ideals, etc.). Things get nasty when you are interested in rings with unity and start considering homs which don't preserve them (e.g. direct limit of rings with unity won't even have to have unity).  >> Anonymous Mon Oct 30 13:37:12 2017 No.9265827 >A separator N is minimal if N\{i} is not a (k, x)-separatorWhat does N\{i} means in mathspeak? N is a subset.  >> Anonymous Mon Oct 30 13:37:32 2017 No.9265828 >>9263958be warned that throughout wikipedia, the incorrect definition of a ring is used (although to its credit it does specify that there is one other (the correct) definition of rings, which it does not use).  >> Anonymous Mon Oct 30 14:03:00 2017 No.9265858 Alright sciHelp me with this exam problem"Find the volume by rotating the region bounded by $y = cos x$ and $y = x$ around the x-axis." No calculators, no shit. How can I solve this?  >> Anonymous Mon Oct 30 14:21:57 2017 No.9265899 >>9265827N excluding i. The subset of N containing all elements of N but i.  >> Anonymous Mon Oct 30 14:32:02 2017 No.9265915 >>9265533>No lecture is ever better than a textbook.Which college for brainlets do you go to?  >> Anonymous Mon Oct 30 15:00:46 2017 No.9265963 In probability, if a question asks something like:"What is the probability of x happening *at least once*?"does this include it happening 0 times?So for instance A = a man his a target at least once.P(0 hits) = 0.2963)P(1 hit) = 0.4444Would P(A) = 0.2963 + 0.4444?  >> Anonymous Mon Oct 30 15:01:26 2017 No.9265966 >>9265963>In probability, if a question asks something like:>"What is the probability of x happening *at least once*?">does this include it happening 0 times?No, that would be "at most once" (<=1)At least once is (>=1)  >> Anonymous Mon Oct 30 15:02:19 2017 No.9265971 >>9265966At most once is what I meant shitSo 0.2963 + 0.4444 is at most once right?  >> Anonymous Mon Oct 30 15:03:20 2017 No.9265973 >>9265971>So 0.2963 + 0.4444 is at most once right?Yes.  >> Anonymous Mon Oct 30 15:04:46 2017 No.9265978 Was just offered a job In Oklahoma$65k base pay once I graduate this coming December. Ill have to leave all my friends and family though. Is the money worth it.
 >> Anonymous Mon Oct 30 15:06:56 2017 No.9265983 >>9263958how many golf balls to equal the mass of the sun in kilograms?
 >> Anonymous Mon Oct 30 15:10:15 2017 No.9265987 >>92659831.989e30 kg/0.04593 kg
 >> Anonymous Mon Oct 30 15:14:15 2017 No.9265997 >>9265915All universities are filled with brainlets (the only difference is their parents' money) and professors have to deliver to them.
 >> Anonymous Mon Oct 30 15:15:03 2017 No.9265999 >>9265997>All universities are filled with brainlets (the only difference is their parents' money) and professors have to deliver to them.Which college for brainlets do you go to?
 >> Anonymous Mon Oct 30 15:21:59 2017 No.9266010 >>9265997Imagine believing this.
 >> Anonymous Mon Oct 30 15:22:27 2017 No.9266013 >>9265978Depends on your field of work and how good of a candidate you are; knowing nothing else about you I would take it. 65k in a low-CoL area is pretty good entry-level for the majority of fields and only the top handful of students in each field can really afford to be picky about starting jobs.Relocating after college is almost the norm anymore.
 >> Anonymous Mon Oct 30 15:26:53 2017 No.9266027 >>9265915I really like the MIT lecturesbut it does not have a lot of exercises and problems
 >> Anonymous Mon Oct 30 15:36:13 2017 No.9266044 Is the following true: If $a_n\to a$ as $n\to\infty$ and $\forall n(a_n\in X)$, then $a\in X$?$a_n=1/n\,;\ X=(0,\infty)$ seems like counter example, but i dont know if i'm misunderstanding something
 >> Anonymous Mon Oct 30 15:37:15 2017 No.9266045 >>9266044>an=1/n; X=(0,∞) seems like counter exampleYou are correct.
 >> Anonymous Mon Oct 30 15:38:31 2017 No.9266049 Dumb probability question:$P(A) = 1/3\P(B) = 2/3\{BBB, BBA, ABB} = (\frac{2}{3} ^3) + ((\frac{2}{3} ^2) * \frac{1}{3}) + ((\frac{2}{3} ^2) * \frac{1}{3}) = 0.59332$That's what I got. Is that correct?
 >> Anonymous Mon Oct 30 15:39:48 2017 No.9266051 >>9266049I'm shit at latex{BBB, BBA, ABB} = ...= 0.59323
 >> Anonymous Mon Oct 30 16:14:30 2017 No.9266133 >>9265899Appreciate it anon
 >> Anonymous Mon Oct 30 16:20:58 2017 No.9266147 >>9266044This is true if and only if X (metric space) is closed.For general topological spaces "<=" holds, but not necessarily "=>".
 >> Anonymous Mon Oct 30 16:22:11 2017 No.9266149 >>9266147See also here:https://en.wikipedia.org/wiki/Sequential_space
 >> Anonymous Mon Oct 30 16:29:35 2017 No.9266160 is there anywhere i can ask brainlet-level questions and get a response quickly?the majority of the questions i have are simple yes/no answers but it's always hit or miss here it seems.an irc for it would be perfect.
 >> Anonymous Mon Oct 30 17:16:57 2017 No.9266218 How do you solve a boundary value problem using Green's Function when y(0) = 1 and y'(0) = 0?When I set up my two integrals, what should they be equal to? 0 < t < x and then x < t < 0 i'm pretty sure is wrong.
 >> Anonymous Mon Oct 30 17:49:57 2017 No.9266252 >>9263958Here's my stupid question:The inner Earth is hot because of pressure, right? But how does that not violate the laws of thermodynamics? It just seems like it'll keep creating heat forever without having another energy to turn into it.
 >> Anonymous Mon Oct 30 18:36:18 2017 No.9266305 File: 41 KB, 483x473, 1506616234119.jpg [View same] [iqdb] [saucenao] [google] I have just begun my study of physics at university level. My professor was not aware Scotland slowed down a photon beam.http://www.bbc.com/news/uk-scotland-glasgow-west-30944584She said to the class that nothing moved faster than the speed of light and that it's speed was constant. My social anxiety made me hold my tongue, but I later emailed the article to her to show her that is wrong. I realize that classic physics and quantum physics are very different fields, but this woman has a masters and was unaware of the fact. She later told us that Newton's equation for gravity was also wrong and offered Einstein's which is based on light being constant. My question for anyone who has pursued physics is to what extent am I going to be learning things during my studies of physics which are fundamentally wrong? What are those things? >>TL;DR What basic physical principles or equations taught early on in college are wrong??
 >> Anonymous Mon Oct 30 18:38:28 2017 No.9266307 >>9266305You literally just said classic and quantum are two different fields. Do you even know what the two are? Start there.
 >> Anonymous Mon Oct 30 18:47:31 2017 No.9266331 (n^2−1)=(n−1)(n+1) Can you prove it?
 >> Anonymous Mon Oct 30 18:51:32 2017 No.9266337 >>9266331just expand (n-1)(n+1) brainlet
 >> Anonymous Mon Oct 30 18:59:50 2017 No.9266356 >>9265543Adderall.
 >> Anonymous Mon Oct 30 19:00:01 2017 No.9266358 >>9266337I get the factoring I’m just asking why one less than a number squared is equal to the product of one more than and one less than that number
 >> Anonymous Mon Oct 30 19:00:25 2017 No.9266359 >>9264484(on non-compact spaces)
 >> Anonymous Mon Oct 30 19:04:00 2017 No.9266366 >>9266358just expand the product of one more than and one less than that number brainlet
 >> Anonymous Mon Oct 30 19:05:57 2017 No.9266373 >>9264413Actually in the trivial ring $\{0\}$, zero is both the mutiplicative unit and the additive unit. (it's a shit ring to begin with but that doesn't stop it from having this property, it's the only ring that can have this property).
 >> Anonymous Mon Oct 30 19:06:51 2017 No.9266376 >>9266331Brah
 >> Anonymous Mon Oct 30 19:07:19 2017 No.9266378 >>9266373>Actually in the trivial ringYou are trivial.
 >> Anonymous Mon Oct 30 19:07:53 2017 No.9266381 >>9266366Feeling repetitive? Maybe you can use words to convince me that this is so.
 >> Anonymous Mon Oct 30 19:08:15 2017 No.9266383 >>9264484You are being a cunt. There are plenty of text that (espec older) that don't define rings as having multiplicative units. Thats why most texts that deal with rings says things like "in this text we will by a ring mean a ring with a multiplicative unit, unless otherwise specified".
 >> Anonymous Mon Oct 30 19:14:27 2017 No.9266400 where would be a good place to learn about image recognition, for practical purposes? I'm primarily interested in simple geometric shapes and colors. The most computer science I know is Java, so when I tried to read wikipedia it was too much new information to get anything useful out of
 >> Anonymous Mon Oct 30 19:20:23 2017 No.9266413 >>9266358Make a n+1 by by n-1 square grid with dots. (e.g. 5 from left to right, 3 from top to bottom).Remove the first row (n+1 dots) and adjoin it vertically next to the first column (n-1 dots).Now you have a n by n grid with 1 dot sticking out.Therefore (n-1)(n+1)=n^2+1.Ο.Ε.Δ.
 >> Anonymous Mon Oct 30 19:21:39 2017 No.9266418 >>9266413>no inductionWrong.
 >> Anonymous Mon Oct 30 19:22:27 2017 No.9266419 >>9264722so explain black holes and infinite mass. wouldn't that mean infinite gravity?
 >> Anonymous Mon Oct 30 19:36:56 2017 No.9266449 >>9266413Not bad. Good job.
 >> Anonymous Mon Oct 30 19:37:52 2017 No.9266451 I am not a physicist so I won't ask about explaination. From pop science it seems many worlds is more popular amongst physicists than the Copenhagen interpretation. My question for you all is: is that an accurate picture to paint?It just seems more complicated without explaining anything additional.
 >> Anonymous Mon Oct 30 19:39:41 2017 No.9266455 I got a question for all yall smart motherfuckers.. Need only the smartest neebas on this board to answerIs it possible that a two dimensional being(s) exist? if yes, could they probably get addicted to drugs?
 >> Anonymous Mon Oct 30 19:48:07 2017 No.9266463 >>9266455This question lacks depth
 >> Anonymous Mon Oct 30 19:49:50 2017 No.9266466 >>9266463i said smartest people on the board, answer
 >> Anonymous Mon Oct 30 19:52:54 2017 No.9266470 How do I find the best possible item given multiple factors and varied importance of said factors?Let's say I'm grading apples by Redness, Sweetness and Size. The scales are arbitrary (Redness 0-10, Sweetness -200 - 200, Size 1-100), and each factor is weighted differently (Sweetness is 30% more important than Size, which is 50% more important than Redness).I want to give each apple a final score that correctly describes this relationship, so that I can mathematically pinpoint which apple is closest to perfect.How do?
 >> Anonymous Mon Oct 30 20:09:50 2017 No.9266494 >>9266470you could reduce everything to a common variable then optimize it
 >> Anonymous Mon Oct 30 20:11:51 2017 No.9266498 File: 985 KB, 1034x1989, babaa_scattering.png [View same] [iqdb] [saucenao] [google] >>9265707Something like $\overleftrightarrow{\partial}$? This means [eqn]\hat\psi \overleftrightarrow \psi = \hat\psi \partial \psi + (\partial \hat\psi)\psi[/eqn]
 >> Anonymous Mon Oct 30 20:19:10 2017 No.9266509 >>9266498Meant $\hat\psi \overleftrightarrow{\partial}\psi$ on the left.
 >> Anonymous Mon Oct 30 20:19:24 2017 No.9266510 >>9266494I'm not sure how to go about doing that, and I'm going to need it to be tweakable. Preferably something I can do algorithmically, because I'm not 100% decided on what the weights of the variables are going to be, and I'll need to see how things shake out as I tweak things.I feel like simply reducing the variables is an over-simplification that won't properly express the data, but I could be wrong.
 >> Anonymous Mon Oct 30 20:24:24 2017 No.9266522 Been working on this for a little while. Starting to feel like I'm at the end of my rope...I was able to reduce it to [eqn]1/(2*\sqrt{3}*\pi)\int_{-\infty}^{+\infty}\int_{-\infty}^{+\infty} e^{-1/3(x^2 -xy + y^2 -2y +1)}dxdy = 1/2 \int_{-\infty}^{+\infty}e^{-1/3(x(x-u)}dx[/eqn]where [eqn] u = y-1[/eqn]But I'm wondering now whether I'm even on the right track
 >> Anonymous Mon Oct 30 20:26:18 2017 No.9266524 File: 40 KB, 813x250, Screenshot_41.png [View same] [iqdb] [saucenao] [google]
 >> Anonymous Mon Oct 30 20:27:22 2017 No.9266527   >>9266522Sorry, this should read[eqn]1/(2\sqrt{3}\pi)\int_{-\infty}^{+\infty}\int_{-\infty}^{+\infty} xe^{-1/3(x^2 -xy + y^2 -2y +1)}dxdy = 1/2 \int_{-\infty}^{+\infty}e^{-1/3(x(x-u)}dx[/eqn]where [eqn] u = y-1[/eqn]
 >> Anonymous Mon Oct 30 20:29:02 2017 No.9266532 >>9266522Should actually read[eqn]1/(2\sqrt{3}\pi)\int_{-\infty}^{+\infty}\int_{-\infty}^{+\infty} e^{-1/3(x^2 -xy + y^2 -2y +1)}dxdy = 1/2 \int_{-\infty}^{+\infty} x e^{-1/3(x(x-u)}dx[/eqn]where [eqn] u = y-1[/eqn]
 >> Anonymous Mon Oct 30 20:29:05 2017 No.9266533 >>9266527>>9266522Why is there a u in the right hand side but no du?
 >> Anonymous Mon Oct 30 20:30:28 2017 No.9266537 >>9266533I integrated out the integral with respect to y - 1 = u
 >> Anonymous Mon Oct 30 20:37:05 2017 No.9266548 >>9266537>I integrated out the integral with respect to y - 1 = uWhy is there a u in the right hand side if you already integrated with respect to u?
 >> Anonymous Mon Oct 30 20:45:07 2017 No.9266571   >>9266548Because I rearranged the equation with a term of the form [eqn] \int_{-\infty}^{+\infty}\int_{-\infty}^{+\infty} \frac{1}{2\sqrt{3}\pi }e^{-\frac{1}{3}x(x-u) + u^2} dxdu [/eqn]
 >> Anonymous Mon Oct 30 20:46:09 2017 No.9266575 I rearranged it to look like this:[eqn] \int_{-\infty}^{+\infty}\int_{-\infty}^{+\infty} \frac{1}{2\sqrt{3}\pi }e^{-\frac{1}{3}(x(x-u) + u^2)} dxdu [/eqn]
 >> Anonymous Mon Oct 30 20:58:04 2017 No.9266588 >>9264158yes, exactly what you wrote... how does the b go there?
 >> Anonymous Mon Oct 30 21:07:45 2017 No.9266603 s\pw %$t\vpw pw\}pw (~{\{p\rwtt |~p$x s\pw *tw\wt$}t\pw$\ypw p\rwx} %{~\rwx} rw&~ spw\}t$\%$p pw\}pw (~{\{p\rwtt qx\$~\sxw r{p\vx\pxw s+tw (~{\{p\rwtt vpw *tw\wt$ p\rwx} ytwp }t\pw$\ypw spw\}t$\%$p z{t$w %wp}\+xt (~{\{p\rwtt vpw s\pw p\rwx p\rwx} z{x++xt s\pw %{~\rwx} rw&~ }p$w\s~xt\%$~ p\zwp }~\sp\xw vpw *tw\wt$sxqtw %$t\vpw p\zwp pw\{~$+ p\rwx p\rwx} qp\v~$wx spw\}t$\%$p pw\ypw qt\{p\$p}p sxqtw pw\ypw %$t\}x{{ |p\t s\pw pw\ypw vpw (~{\{p\rwtt qt s+tw |~p$x }p$w\s~xt\%$~ %zx} p\rwx} pw\}pw spw\}t$\%$p pw\ypw p\ztw\sx\v{x}x %zx} p\ztw\sx\v{x}x (~{\{p\rwtt }p$w\s~xt\%$~Need help with this cypher because I'm a brainlet. Any help?  >> Anonymous Mon Oct 30 21:08:50 2017 No.9266604 >>9266603>s\pw %$t\vpw pw\}pw (~{\{p\rwtt |~p$x s\pw>*tw\wt$ }t\pw$\ypw p\rwx} %{~\rwx} rw&~>spw\}t$\%$p pw\}pw (~{\{p\rwtt qx\$~\sxw>r{p\vx\pxw s+tw (~{\{p\rwtt vpw *tw\wt$>p\rwx} ytwp }t\pw$\ypw spw\}t$\%$p z{t$w>%wp}\+xt (~{\{p\rwtt vpw s\pw p\rwx p\rwx}>z{x++xt s\pw %{~\rwx} rw&~ }p$w\s~xt\%$~>p\zwp }~\sp\xw vpw *tw\wt$ sxqtw %$t\vpw>p\zwp pw\{~$+ p\rwx p\rwx} qp\v~$wx>spw\}t$\%$p pw\ypw qt\{p\$p}p sxqtw pw\ypw>%$t\}x{{ |p\t s\pw pw\ypw vpw (~{\{p\rwtt qt>s+tw |~p$x }p$w\s~xt\%$~ %zx} p\rwx}>pw\}pw spw\}t$\%$p pw\ypw p\ztw\sx\v{x}x>%zx} p\ztw\sx\v{x}x (~{\{p\rwtt>}p$w\s~xt\%$~That's not a cypher, it's just jibberish.
 >> Anonymous Mon Oct 30 21:11:26 2017 No.9266608 >>9266604I wouldn't be so sure. Also, the hint included is Ouroboros
 >> Anonymous Mon Oct 30 21:11:41 2017 No.9266609 >>9266608>I wouldn't be so sure.I am.
 >> Anonymous Mon Oct 30 21:15:57 2017 No.9266613 >>9266609I'll take your word for it.
 >> Anonymous Mon Oct 30 21:31:55 2017 No.9266633 Can somone give me the homotopy?
 >> Anonymous Mon Oct 30 21:34:19 2017 No.9266638 File: 2.69 MB, 4224x3136, IMAG0120.jpg [View same] [iqdb] [saucenao] [google] >>9266633Forgot pic.
 >> Anonymous Mon Oct 30 21:34:38 2017 No.9266642 File: 212 KB, 645x960, test (6).jpg [View same] [iqdb] [saucenao] [google] >>9266633Sorry only got holonomy here.
 >> Anonymous Mon Oct 30 21:58:32 2017 No.9266678 Does $x\cdot|x|=x^2$?
 >> Anonymous Mon Oct 30 21:59:30 2017 No.9266680 >>9266678nope. sps x = -1
 >> Anonymous Mon Oct 30 22:06:41 2017 No.9266690 https://youtu.be/6NB67n9q8NQ?t=465why does it shatter like this? after being shot so many times, eventually it shatters like glass.first it bends, then it shatters. it's like a cross between metal and glass. Is it better for body armor to be crystalline or amorphous and which one is this?
 >> Anonymous Mon Oct 30 22:09:18 2017 No.9266692 >>9266638That's a deformation retract of a doubly punctured disc and deformation retracts don't affect the homotopy.$\pi_1(D \setminus \{x_1,x_2\}) = \pi_1(S^1 \wedge S^1) \cong \mathbb{Z} \otimes \mathbb{Z}$
 >> Anonymous Mon Oct 30 22:12:46 2017 No.9266696 >>9266692Do you mean Z+Z ?
 >> Anonymous Mon Oct 30 22:14:59 2017 No.9266698 >>9266692>>9266696I´m actually in intro to complex analysis and I don't have a single clue about algebraic topology, but I have an exercise In which I need to construct a homotopy bewteen the bigger circle and the smaller one. I just have in the bag the definition of it.
 >> Anonymous Mon Oct 30 22:15:45 2017 No.9266700 Has anyone taken the GMAT? How difficult is the math?Should I go back and review holistically (I haven't done anything related to higher math in around a decade) or should I study specifically for the test?
 >> Anonymous Mon Oct 30 22:17:08 2017 No.9266701 File: 212 KB, 341x444, ran_srs.png [View same] [iqdb] [saucenao] [google] >>9266696No. I meant the free group upon by 2 elements.>>9266698>actually construct the homotopyDo people actually still do this?
 >> Anonymous Mon Oct 30 22:30:14 2017 No.9266714 >>9266701Ok but you wrote the tensor product, which isn't right.
 >> Anonymous Mon Oct 30 22:34:27 2017 No.9266720 >>9266701I suppose it's just a non trivial constructión in this case. My problem is that the just uses the convex sum of the curves but it gives a weird parametrization of the unit circle so it has some weight in the parameter. Basically he first finds a $k, \vert \frac{1}{2}+ke^{is}\vert^2=1$ which gives $k=\frac{\sqrt{cos^2s+3}-coss}{2}$ But this only works for $s\in [0,\pi/2]$. Then I'm asked to construct the parametrization for $s\in [\pi/2,\pi]$ Which I belive needs to have a similar weight, but in $\gamma(s)=1$ which overshoots as I belive the points directly above the inner curve needs to go at the same rate as the normal parametrization of each component of that inner curve as in the section $[o,\pi/2]$ the book gives your typical circle parametrization.I'm at a loss.
 >> Anonymous Mon Oct 30 22:49:50 2017 No.9266742 File: 2 KB, 288x216, paint.png [View same] [iqdb] [saucenao] [google] >>9266413Oh wait I fucked up. That's not correctTake from the row/column with the n-1 dots. Adjoin to the column/row of the n+1 dots. If you add a new dot then you get a n by n grid.
 >> Anonymous Mon Oct 30 23:10:27 2017 No.9266767 >>9266680what?
 >> Anonymous Mon Oct 30 23:11:56 2017 No.9266770 Why do radiography courses take 3+ years? I know colleges like to drag shit out for money but it seems excessive.
 >> Anonymous Mon Oct 30 23:19:30 2017 No.9266781 >>9266638The reason for this being ZxZ is because you have two holes you can loop around. It's that simple. If you take any loop then you can deform it to any other loop that goes around the two different holes the same number of times.
 >> Anonymous Mon Oct 30 23:28:00 2017 No.9266788 >>9264316it can be derived from the original definition of the factorialf(x+1)=f(x)(x+1) given f(1)=1f(0+1)=f(0)(0+1)f(1)=f(0)(1)1=f(0)god i need to learn Latexyou can also define it from the Gamma Function tho, Id guess that someone found it from the recursive definition before someone even found the Gamma function
 >> Anonymous Mon Oct 30 23:30:13 2017 No.9266791 >>9266767If x=-1 that equality doesn't hold.
 >> Anonymous Mon Oct 30 23:39:59 2017 No.9266802 >>9266455its impossible for 2 dimensional beings to exists in our universe
 >> Anonymous Tue Oct 31 00:02:36 2017 No.9266817 >>9263958how come everyone can see the moon at night? how fast does the moon orbit the earth? does it orbit the earth at an opposite direction to earths rotation? if there is a slar eclipse then what happens with the side of the earth where its currently night time, is the moon visible?Imean it has to orbit in an opposite direction or a completely different speed otherwise the moon would be onlky visible at some places, what happens t the poles? is the moon always visible there? is it never visible there? none of this makes sense to me how does the moon really work?
 >> Anonymous Tue Oct 31 00:04:08 2017 No.9266819 >>9266788learning latex is easy and fun to do! I recommend it.t. brainlet who can't even code but is competent in tex
 >> Anonymous Tue Oct 31 00:05:45 2017 No.9266823 >>9266817come to think of it how the fuck is mercury visible at all
 >> Anonymous Tue Oct 31 00:07:10 2017 No.9266824 >>9266817It takes 27 days for the moon to rotate around the Earth once (sidereal month).The moon orbits in the same direction as the Earth rotates. The moon is not visible from the night side of the Earth during a solar eclipse. I think the axial tilt (and the orbit of the moon) makes it so the moon does not rise at certain times of the year at the poles.
 >> Anonymous Tue Oct 31 00:08:31 2017 No.9266826 >>9266823certain times of the year Mercury is visible for a short period of time just before the sun comes up (in the northern hemisphere, maybe in the southern too) It's like only half an hour or something
 >> Anonymous Tue Oct 31 00:09:09 2017 No.9266828 >>9266824you didnt answer the most important question
 >> Anonymous Tue Oct 31 00:09:50 2017 No.9266829 >>9266828Which one?
 >> Anonymous Tue Oct 31 00:13:09 2017 No.9266831 >>9266829how come the moon is always visible at night anywhere but the poles unless there is a solar eclipseisit just a coinsidence because it has the perfect speed to always be at the oposite end to the sun?that doesnt make sense either, if it rotates then there should always bee solar eclipses because it must constantly cross paths with the sun
 >> Anonymous Tue Oct 31 00:13:44 2017 No.9266833 >>9266824The term of art is /prograde orbit/, as opposed to retrograde.
 >> Anonymous Tue Oct 31 00:14:26 2017 No.9266834 >>9266831* there hould be at least one solar eclipse every 27days
 >> Anonymous Tue Oct 31 00:16:41 2017 No.9266841 >>9266831The orbit of the moon is tilted relative to the ecliptic (the earth-sun orbit) so a total solar eclipse is only possible twice a year and because of the eccentricity of the Moon's orbit a real total solar eclipse happens even less often (iirc)
 >> Anonymous Tue Oct 31 00:18:00 2017 No.9266843 I know for PhD applications that research experience and letters of recommendation are the most important, with GPA and GRE score being slightly less important, but how is it for MS applications? I've heard research isn't required, but does it significantly help to have research experience over other applicants? Or is it actually just grade based and some teacher saying "yeah he was a good student sure"
 >> Anonymous Tue Oct 31 00:19:55 2017 No.9266845 >>9266841ok but hear me outin order to see the moon at night the moon must be at the opposite side of the planet to the side thats iluminated by the sun at all timesotherwise there would be a lot of moonless nights
 >> Anonymous Tue Oct 31 00:20:01 2017 No.9266846 >>9266843All graduate programs I've seen need at least two letters or recommendation and a certain average, that's the bare minimum
 >> Anonymous Tue Oct 31 00:22:17 2017 No.9266849 >>9266845There are moonless nights, it's called the new moon phase
 >> Anonymous Tue Oct 31 00:23:37 2017 No.9266852 >>9266849i feel stupid for never notticing this
 >> Anonymous Tue Oct 31 00:25:55 2017 No.9266856 >>9266852Don't I'm puzzling over it a bit too, it seems like there would be more moonless nights than just one a month
 >> Anonymous Tue Oct 31 00:29:24 2017 No.9266864 >>9266856also how is it always the same cycle? we dont use a moon based calendar
 >> Anonymous Tue Oct 31 00:32:59 2017 No.9266872 >>9266864what are you asking? And we kind of do use a moon based calendar, a sydonic month (like 31 days) is how long it takes for the moon to show the same phase and is longer than a sidereal (star) month (27 days). The months just have different lengths so they can add up to 365 (plus some) days a year (I think).
 >> Anonymous Tue Oct 31 00:35:42 2017 No.9266874 >>9266872the sydonic months are probably totally out of phase with the calendar months now but not in ancient times
 >> Anonymous Tue Oct 31 00:36:20 2017 No.9266875 >>9266872it makes sense if its a moon based calendar, otherwise we could get two moonless nights some years in october because its 31 days long and it takes 27 days to orbit the earth
 >> Anonymous Tue Oct 31 00:39:28 2017 No.9266881 >>9266875I'm not actually sure if it's possible to show two of the same phases in one month but it seems like something that happens like once every 200 years or something
 >> Anonymous Tue Oct 31 03:13:02 2017 No.9267053 >>9266470>>9266494Since there were many more than three variables in my data set, and at least two of them were somewhat subjective, the solution turned out to be a modified version of Analytic Hierarchy Process. I wrote a quick program to calculate the weighted and unweighted averages of various variable pairs, and then the pairs against one another, and then had it iterate through a few thousand times while scaling the subjective variables back and forth across reasonable bounds.A clear pattern of best options emerged from the data points I shotgunned against the wall, and subsequent testing backs up the results.I still wish I knew a clean and quick way to do this as it's not exactly something I could do on the back of a napkin - but when it doubt, brute force it out.
 >> Anonymous Tue Oct 31 06:47:33 2017 No.9267202 >>9265858Pls halp
 >> Anonymous Tue Oct 31 06:51:51 2017 No.9267212 >>9267202Ops I forgot to say that x >= 0
 >> Anonymous Tue Oct 31 06:53:41 2017 No.9267215 >>9263958This is one of the best threads on the internet. It has greatly helped me in the past. It's not much of a reward, but I want to thank all you faggots ITT and in past threads that help us brainlets.
 >> Anonymous Tue Oct 31 07:07:00 2017 No.9267229 In which position would I have to deal with more egotistical fuckwit coworkers, doctor or rad tech?
 >> Anonymous Tue Oct 31 07:42:34 2017 No.9267266 How would you find out of two events are independent of each other using just the content of their sets?I.e. not by using their probabilities
 >> Anonymous Tue Oct 31 07:57:01 2017 No.9267275 >>9267202>>9267212Use cylindrical coordinates (considering the x-axis as the z-axis; z_o is the first positive solution of z = cos(z)) [eqn] V = \int \limits_{\theta = 0}^{2 \pi} \int \limits_{z = 0}^{z_o} \int \limits_{\rho = z}^{\cos z} \rho \,d \rho \,dz \,d \theta [/eqn] Not sure if it's correct but you'll get something similar anyway.
 >> Anonymous Tue Oct 31 09:27:10 2017 No.9267378 >>9267275I'm sorry but I don't understand your solutionI don't know how to do 3 integrals at the same time tooI know basic integral (trig substitution, u substitution, etc)
 >> Anonymous Tue Oct 31 09:35:43 2017 No.9267388 >>9267378it's just a fancy way of writing the washer method, he didn't solve what the hell x = cosx is which is really the true kicker to the problem, best I can do is approximate it as sqrt(3)-1, and after briefly looking around online , that seems to be the best you're going to get
 >> Anonymous Tue Oct 31 10:15:57 2017 No.9267437 File: 37 KB, 500x495, 1499723660864.jpg [View same] [iqdb] [saucenao] [google] I am 1/4 way through my masters.I am getting scared it is ending too soon.One way of stalling is to do an honors for my undergraduate.It would give me an addition dissertation+4 more elective units from my specialization.It would take an extra year of my time (good/neutral)and cost my \$6000 (kind of bad).Should I do it, I don't think I wan to go into the real world yet.
 >> Anonymous Tue Oct 31 10:46:11 2017 No.9267477 suppose $f : E \rightarrow F$ and $g : F \rightarrow E$, if $(f \circ g \circ f)$ is a bijection, is $f$ a bijection? How does one prove this?>>9265451Is this a coincidence or were you sitting in the same lecture hall as I was, scratching your head when the prof said this was trivial...?At least ask the question right, you clucker.
 >> Anonymous Tue Oct 31 11:29:19 2017 No.9267528 >>9267477Let's prove an equivalent proposition: if f is not a bijection, then fogof is not a bijection.If f is not injective, then for distinct x,y in E you have f(x)=f(y), which means gof(x)=gof(y) and fogof(x)=fogof(y), so fogof is not injective and therefore not bijectiveIf f is not surjective, then there are elements in the codomain which are not in the image of f, so fogof is not surjective and therefore not bijective.
 >> Anonymous Tue Oct 31 11:32:35 2017 No.9267532 >>9267266If their intersection is the null set.
 >> Anonymous Tue Oct 31 11:59:23 2017 No.9267561 >>9267532It's not. One is a subset of the other. (A {a,b,c}, B{a.b.c.d})Does that mean they are dependent on one another?
 >> Anonymous Tue Oct 31 12:01:06 2017 No.9267564 >>9267437Real life is 10x better than school.
 >> Anonymous Tue Oct 31 12:16:24 2017 No.9267592 Do quantum mechanics imply the universe is not deterministic?As I have understood it, with my bias, that "non-determinism" is only relevant or true when it comes to our attempts to measure/observe events.But many people seem to say that there really is "non-determinism". That truly random events and non-causal outcomes happen in reality. What's the truth about this? Is the universe really "random"?
 >> Anonymous Tue Oct 31 12:20:52 2017 No.9267600 >>9267388I guess the question is wrong then. Thank you, anon
 >> Anonymous Tue Oct 31 12:23:29 2017 No.9267610 >>9267561If event A is a subset of event B then event B happening implies event A happens so they are dependent (but only one way)
 >> Anonymous Tue Oct 31 12:27:50 2017 No.9267612 >>9267532If their intersection is empty, then they are dependent as fuck. One event happening excludes the other.
 >> Anonymous Tue Oct 31 12:37:59 2017 No.9267616 >>9267612>One event happening excludes the other.that's what independent means iircam I wrong?
 >> Anonymous Tue Oct 31 12:41:27 2017 No.9267625 >>9267561Yes of course they are.Generally, two events A and B are dependent if and only if one gives information about the other.i.e. P(A happening given B happening) is not equal to P(A happening) or equivallently P(B given A) is not equal to P(B).
 >> Anonymous Tue Oct 31 12:42:29 2017 No.9267626 >>9267616>am I wrong?yeah, see >>9267625
 >> Anonymous Tue Oct 31 14:09:35 2017 No.9267772 Did a simple Baye's problem for a question, but the third part is basically doing it backwards. In short:P(A) = 1/3P(B) = 2/3P(C|A) = 1/10P(C|B) = 1/5P(C) = (totality) = 0.1666But the third part has said P(C) is revised to 1/8.How would P(A) and P(B) be revised to account for this, assuming P(A) must have the "smallest proportion" out of A and B?I'm guessing that means P(A) must be the smallest possible amount.
 >> Anonymous Tue Oct 31 18:01:08 2017 No.9268170 File: 37 KB, 604x116, p7.png [View same] [iqdb] [saucenao] [google] Can anyone help me with this proof. I know with the hints it should be easy. It is a stupid question thread after all.So my plan was to assume the worst possible case.A stack of n pancakes in which none of them can be glued together.Does anyone have any resources that might be helpful for the pancake problem or pancake numbers?
 >> Anonymous Tue Oct 31 19:06:38 2017 No.9268260 do axiomatic systems exist in which a finite number of theorems can be derived?
 >> Anonymous Tue Oct 31 19:11:56 2017 No.9268267 >>9264775The point of what he said is that there is no purpose to life. Make one your own, but it isn't going to matter.
 >> Anonymous Tue Oct 31 19:24:04 2017 No.9268291 >>9268260sure, but only in a very abstract sense.You can think of any rewrite system as an "axiomatic system", and think of any "derivable expression" as a "theorem". In that sense, you could make an "axiomatic system" which just has a start symbol S which rewrites as any number of things in a finite list, and that gives an example.In practice though, no. Even if your logic just has conjunction, if you can prove phi, you can prove phi & phi, phi & phi & phi, etc. though maybe you are really interested in something weaker, like "finite number of theorems, mod being provably equivalent". Then again, yes, just take any classical propositional logic with only finitely many propositions.
 >> Anonymous Tue Oct 31 20:27:40 2017 No.9268365 >>9266419Black holes don't have infinite mass.
 >> Anonymous Tue Oct 31 22:07:53 2017 No.9268475 Ok /sqt/ I'm fucking stupid at Linear AlgebraI don't understand Vector Spaces and all of this shitPlease help. Do you guys knows a good book/lectures/whatever to help me?I tried MIT lectures but I don't understood them
 >> Anonymous Tue Oct 31 22:12:40 2017 No.9268483 >>9268475>I tried MIT lectures but I don't understood themThat's because they are shit.Try Axler's book. It's really well-written.
 >> Anonymous Wed Nov 1 00:49:06 2017 No.9268641 >>9264006You guess. That's it. You need it to dominate the original function to actually interchange limits but that's usually not a problem.
 >> Anonymous Wed Nov 1 02:18:59 2017 No.9268698 >>9266305They're all wrong since we don't have a set of postulates that predicts all physical phenomena yet. Also nothing moves faster than light in a vacuum. Light slows down in air because it can no longer move in a straight line. It bounces around so it "travels" slower through it.
 >> Anonymous Wed Nov 1 03:00:22 2017 No.9268720 >>9264723I recently read something interesting that ties into this so I'm sharing it. Imagine the food chain before humans asserted themselves into the top of it.The lion hunts down and eats 80% (I'm pulling the number out of my ass) of the meat.Vultures eat the remaing 19%.How can humans survive if other predators have clear advantages? A lion can run behind and kill with its teeth, the vulture can pick up left meat from the ground and get away without much trouble. The human? The human does not have sharp teeth or wings, but he uses tools to break into the left bones of animals, which contain inside bone marrow, a food source that is not exploited by other predators. After humans started to use their intelect instead of instincs to be better predators they asserted themselves into the top of the food chain.That is your purpose. As a human your purpose in life is to use tools in order to break into bones of animals. Or at least was until we, not only asserted ourselves into the top, but also made sure to get a limitless amount of food that is easily accesible, effectively eliminating our purpose in life. Now because we are the animal on top, and the one who does not worry as others of survival, your purpose in life is whatever challenge/goal you set yourself. Anon, remember that the greatest gift in life is the chance to make a difference, no matter how small or big impact you think it will have, it is a great gift. Have that in your heart and when you are given the magnificent gift do not shy away from it.
 >> Anonymous Wed Nov 1 03:27:37 2017 No.9268737 Some time ago an anon here was posting some art related to topology. For example, one of them was a hand covered with holes. It was titled cohomology or something like that. Does anyone have a link to those pictures?
 >> Anonymous Wed Nov 1 03:38:59 2017 No.9268743 File: 1.52 MB, 1907x2906, 9r0oMNl.jpg [View same] [iqdb] [saucenao] [google] >>9268737https://imgur.com/r/math/vJX89Fomenko's "A space with nontrivial local homology" [1967]
 >> Anonymous Wed Nov 1 03:42:20 2017 No.9268746 >>9268743Holy shit that was fast. Thanks a lot!
 >> Anonymous Wed Nov 1 04:00:16 2017 No.9268760 File: 95 KB, 852x591, ada.png [View same] [iqdb] [saucenao] [google] Can anybody help me understand the proof of 1)? Why does this prove that the pre image of Q is finite?Alternatively, can anybody link me a good proof for the Riemann-Hurwitz Genus-Degree formula?
 >> Anonymous Wed Nov 1 04:57:42 2017 No.9268802 >>9268760Maybe f mapping infinitely many points into point means it is constant?Or: The last statement says that the infinite subsequence {P_n_i} which are all distinct converges to P. Then for P_a \neq P_b \neq P, we have P \in Neighborhood(P_a) and P \in Neighborhood(P_b). But these are Riemann surfaces which must be Hausdorff, so distinct points must have disjoint neighborhoods. This is a contradiction.
 >> Anonymous Wed Nov 1 05:11:52 2017 No.9268815 Say I have two rows of data, one with the success rates of certain tests and the other with the number of attempts, how would I measure the quality of the results in a way that lets me identify the test that worked "best"? For example>Test 1: 50% success rate, 250 attempts>Test 2: 60% success rate, 100 attempts>Test 3: 55% success rate, 500 attemptsTest 2 has the highest success rate, but fewest attempts, so the results may be less meaningful than those of Test 3.
 >> Anonymous Wed Nov 1 05:44:08 2017 No.9268844 File: 103 KB, 720x478, dardy as boa.jpg [View same] [iqdb] [saucenao] [google] Are sample proportions and binomial distributions essentially the same thing? How do they differ?
 >> Anonymous Wed Nov 1 06:02:05 2017 No.9268858 >>9263958What's a good book to learn complex analysis? I'm a physics student not a math student so I don't know shit about topology
 >> Anonymous Wed Nov 1 07:45:56 2017 No.9268934 What was the name of that bacteria that was supposed to have a different element in its DNA?(I know the experiment was done wrong)
 >> Anonymous Wed Nov 1 08:05:33 2017 No.9268945 HOW I GET MOTHS OUT MY ASS
 >> Anonymous Wed Nov 1 08:36:10 2017 No.9268969 >>9268945Find a natural predator for moths and stick it inside your ass, once it's done pull it out.
 >> Anonymous Wed Nov 1 09:12:50 2017 No.9269001 >>9265451What if f isn't injective? What can you say about fgf? What if f isn't surjective?
 >> Anonymous Wed Nov 1 09:51:49 2017 No.9269030 Is there some operator like modulo, but there aren't any zeros outputted?Rather than (with 1 to 6, m = 6)0 1 2 3 4 5 0 1 2 3 4 5 0 1You get1 2 3 4 5 1 2 3 4 5 1 2 3 4
 >> Anonymous Wed Nov 1 10:29:41 2017 No.9269084 >>9269030modulo + 1
 >> Anonymous Wed Nov 1 10:31:19 2017 No.9269088 >>9269084Yeah I literally just spotted this, fuck me I really am making this a stupid question thread
 >> Anonymous Wed Nov 1 10:33:16 2017 No.9269093 File: 2 KB, 297x297, shitnignog.png [View same] [iqdb] [saucenao] [google] >>9263958so i know that if there is a base, an sn1 can occur, and i will get a racematemy question, is an e2 also possible here?
 >> Anonymous Wed Nov 1 11:18:13 2017 No.9269165 File: 9 KB, 816x1056, what.jpg [View same] [iqdb] [saucenao] [google] what is the length y, which propositions did you use?
 >> Anonymous Wed Nov 1 11:24:55 2017 No.9269174 >>9269093If you use the right base and reaction conditions, sureshit like this is always heavily dependent on the base and reaction conditions used (solvent, temperatur etc)
 >> Anonymous Wed Nov 1 11:26:12 2017 No.9269177 >>9269174thats what i was thinking, thanks babe
 >> Anonymous Wed Nov 1 11:28:03 2017 No.9269179 >>9269177also remember that the preferred conformation of this molecule already has hydrogens in the axial positionsyou have the right geometry aligned already, the problem might just be br- being too good of a leaving group but that should be solveable with the right conditions
 >> Anonymous Wed Nov 1 12:28:10 2017 No.9269264 >>9266305the light went trough a special mask you shithead
 >> Anonymous Wed Nov 1 12:35:32 2017 No.9269276 >>9268844>sample proportionshttp://onlinestatbook.com/2/sampling_distributions/samp_dist_p.html
 >> Anonymous Wed Nov 1 12:52:40 2017 No.9269306 If I have a Set S and this set is empty but I make a Statement about S saying all elements are bigger than 5 is my statement true or false?I could say I cant find an element in S for which that is not the case, hence it's true but I also cant find an element for which that is the case, hence the statement is also false.
 >> Anonymous Wed Nov 1 12:54:28 2017 No.9269311 >>9269306>If I have a Set S and this set is empty but I make a Statement about S saying all elements are bigger than 5 is my statement true or false?https://en.wikipedia.org/wiki/Vacuous_truth
 >> Anonymous Wed Nov 1 12:54:40 2017 No.9269312 >>9269306nevermind I got it myself. The elements for which my statement is true are irrelevant it's about the elements for which it's false
 >> Anonymous Wed Nov 1 12:55:04 2017 No.9269316 Can an Atom of (for example) Carbon which atomic number is 6, have less than 6 neutrons?
 >> Anonymous Wed Nov 1 12:56:55 2017 No.9269323 >>9269311thank you very much
 >> Anonymous Wed Nov 1 13:18:21 2017 No.9269386 Quesstion about solving this differential equation.(D+1)x + (D-2)y = 5/22x + (D-1)y = -2First thing I did was multiply the first equation by -2, then the bottom by (D+1) to cancel out the x.My question is what the fuck is -2(D+1) ?Like what is -2D supposed to be?
 >> Anonymous Wed Nov 1 13:25:13 2017 No.9269393 >>9269386Maybe I didn't study enough math but I'd like to ask wtf is "D+1"? Like, is it "D" as in derivate? Why didnt you put in capital? Usually it's dx + dy = some other shit, but "D+1" is new to me. I did calculus 1 and 2 (still suck at both and didn't pass either exam)
 >> Anonymous Wed Nov 1 13:28:27 2017 No.9269398 >>9269386(D+a)x probably means x'+ax
 >> Anonymous Wed Nov 1 13:37:59 2017 No.9269413 >>9269393It's supposed to be some sort of notation.When you distribute (D+1)x it's Dx +1x, meaning x' + x
 >> Anonymous Wed Nov 1 13:42:01 2017 No.9269422 >>9269398I understand that, but what I still don't know what -2(D+1) is.
 >> Anonymous Wed Nov 1 14:27:02 2017 No.9269497 >>9269422-2(D+1)=-2(d/dt+1)so -2(D+1)f(t)=-2(f'(t)+f(t))=-2f'(t)-2f(t)
 >> Anonymous Wed Nov 1 14:29:17 2017 No.9269502 >>9263958$\color{orange}{\mathfrak{Here's\ a\ stupid\ question}}$$\color{orange}{\mathfrak{Why\ is\ his\ head\ so\ big?}}$
 >> Anonymous Wed Nov 1 14:43:20 2017 No.9269524 >>9269422How can you not?
 >> Anonymous Wed Nov 1 14:48:27 2017 No.9269531 >>9269393That is because a "calculus" course doesn't usually treat a derivative as a linear operator.
 >> Anonymous Wed Nov 1 14:55:58 2017 No.9269549 >>9269531>That is because a "calculus" course doesn't usually treat a derivative as a linear operator.Which college for brainlets do you go to?
 >> Anonymous Wed Nov 1 15:04:34 2017 No.9269570 >>9269549I didn't take calculus at college.
 >> Anonymous Wed Nov 1 15:09:03 2017 No.9269577 File: 32 KB, 620x516, UUbar.png [View same] [iqdb] [saucenao] [google] this is probably what he was going for on the top there
 >> Anonymous Wed Nov 1 15:15:39 2017 No.9269590 >>9269577no. he drew exactly what he wanted. it's a graph with 3 edges and 2 vertices, a contraction of the 2-torus drawn below
 >> Anonymous Wed Nov 1 15:19:34 2017 No.9269600 File: 445 KB, 400x463, EmperorOfManyEmpires.png [View same] [iqdb] [saucenao] [google] >>9269590he drew what he wanted, but what he drew doesn't represent the interaction he's seeking to describe
 >> Anonymous Wed Nov 1 15:40:16 2017 No.9269634 File: 11 KB, 297x109, magic.png [View same] [iqdb] [saucenao] [google] Can anyone see why/how we go from having 2*p*cos(theta) to suddenly having two cosine arguments 3*p*cosine theta - p * cosine theta ?
 >> Anonymous Wed Nov 1 15:41:11 2017 No.9269636 >>9269634> Can anyone see why/how we go from having 2*p*cos(theta) to suddenly having two cosine arguments 3*p*cosine theta - p * cosine theta ?2p=3p-p
 >> Anonymous Wed Nov 1 15:41:55 2017 No.9269638 >>9269636lmao I get itmassive brainlet here
 >> Anonymous Wed Nov 1 16:00:59 2017 No.9269681 Hello /sqt/Are the Multivariable Calculus lectures at MIT OCW good enough? I tried to learn with Stewart book but it is pretty bad (but have good problems)
 >> Anonymous Wed Nov 1 16:08:37 2017 No.9269693 Question about this boundary problem i'm trying to solve.y= c_1x^3 + c_2x^3y(1) = 1 y'(3) = 1I found that c_1 = 1 - c_2 when y(1) = 1I substitute c_1 into y and get y= x^3 - c_2x^3 + c_2x^2What is my first y_1 supposed to be? I'm going to be using that, and then a y_2 from the other value and put it into green's function, but I feel like there's an error here.
 >> Anonymous Wed Nov 1 16:14:37 2017 No.9269709 >>9269681yes, they're good.
 >> Anonymous Wed Nov 1 16:30:34 2017 No.9269735 I need to make a java program that has two methods in a class. One method adds 1 to a string's binary and the other method subtracts 1 from a strings binary.For example, 1011 becomes 1100 when +1 and 1010 when -1.The thing is, we're not allowed to convert anything to integer or use any built in classes other than String.We've not went over anything about binary or binary type problems in class, so I'm not sure where to start here.I found out how to add and subtract binaries on paper. But not being able to convert to anything has me stumped as to what to do.Not looking for the answer, just some help to get started.
 >> Anonymous Wed Nov 1 16:31:49 2017 No.9269736 >>9269179thanks buddy
 >> Anonymous Wed Nov 1 16:43:28 2017 No.9269755 File: 8 KB, 244x206, 1469466916876.jpg [View same] [iqdb] [saucenao] [google] https://proofwiki.org/wiki/Ring_of_Integers_is_Principal_Ideal_Domain/Proof_3what does all the shit about a smallest positive number existing have to do with $\langle b\rangle\subseteq U$?
 >> Anonymous Wed Nov 1 16:51:55 2017 No.9269769 $(0.1 * x) + (0.2 * y) = 0.125$How would I find what x and y are?x needs to be the smallest proportion possible.
 >> Anonymous Wed Nov 1 16:53:46 2017 No.9269773 >>9269755>what does all the shit about a smallest positive number existing have to do with ⟨b⟩⊆U⟨b⟩⊆U?Nothing. But it is required to prove the reverse inclusion, which you would know if you read the next few lines of the proof
 >> Anonymous Wed Nov 1 16:57:09 2017 No.9269781 >>9269773thanks. i thought that but was unsure. would it make a difference if that stuff was written after the first part then?
 >> Anonymous Wed Nov 1 16:59:13 2017 No.9269787 >>9269781Not really
 >> Anonymous Wed Nov 1 17:00:38 2017 No.9269791 >>9269735What I would do under those restrictions for the +1 function would be read the String in reverse order until I find a zero, then save the position where the zero is on an int. That way I have a side of the string which doesn't need to be modified and another side on which I replace the zero for a 1 and all the 1s for 0s.The -1 function is about the same, keep reading zeros until you find a 1.
 >> Anonymous Wed Nov 1 17:07:20 2017 No.9269814 File: 1.48 MB, 1600x1195, ZfqmFfN.jpg [View same] [iqdb] [saucenao] [google] help out a biologie bro heres my thread>>9269801
 >> Anonymous Wed Nov 1 17:25:21 2017 No.9269861 With bayesian spam classifiers, are the features things about the email itself? Or features relating to something else?I've got a question about using naive bayes to discuss a Facebook "interesting post classifier" (i.e. a post is either interesting or not interesting to a user).What would examples of the features be in this case? The words in the post? Or would it also relate to that person's things like their page likes etc?
 >> Anonymous Wed Nov 1 17:40:16 2017 No.9269898 >>9269681Although I heavily dislike Khan Academy, they have a video series on Multivariable calculus where half of it (differentiation part) is made by 3Blue1Brown which is God-tier.
 >> Anonymous Wed Nov 1 18:46:08 2017 No.9270023 File: 3.59 MB, 690x388, green_fire_shorter.gif [View same] [iqdb] [saucenao] [google] Was halfassing some experimentation the last couple of days in prep for Halloween to set up with some green fire for my decorations and kept running into an issue.Stuff I had on hand:>methanol>sodium-tetroborate (borax)>boric acidMixed the methanol with the borax and was getting a orange/red flame from that, where when I did the methanol and boric acid mix I was getting the green flames I desired.With the borax mix am I just running into an issue with sodium contamination and it was overpowering the boron and I need to be using much less borax in my solution?Also I attempted to use sterno cans at one point and had no success with the boric acid or borax, did they change their formulation?Gif is from last night using a.... I think 6 oz of methanol to 1 oz of boric acid powder mixture (think it was an ounce I was kinda doing this freehand and trying not to blow my eyebrows off)
 >> Anonymous Wed Nov 1 18:59:41 2017 No.9270062 I want to learn topology. The highest lvl in math I got to was polar coordinates in calc 2. what/where do i go from there to topology?
 >> Anonymous Wed Nov 1 19:04:22 2017 No.9270071 >>9270062why do you want to learn about topology if you have no experience in real mathematics?If you're convinced: i'd suggest reading something about logic, then modern algebra, then advanced calculus, then analysis, then topology
 >> Anonymous Wed Nov 1 19:09:14 2017 No.9270084 >>9270062analysis is basically calculus made rigorous by using some topology. just grab a real analysis book>>9270071>I want to learn A>I'd suggest learning B, C, D, and then A
 >> Anonymous Wed Nov 1 19:10:11 2017 No.9270088 >>9269316of course it's totally posible
 >> Anonymous Wed Nov 1 19:11:00 2017 No.9270090 >>9270084are you confused?
 >> Anonymous Wed Nov 1 19:12:12 2017 No.9270096 >>9270062Learn some basic analysis on R, then some basic analysis on abstract metric spaces, then general topology, then topology.
 >> Anonymous Wed Nov 1 19:17:34 2017 No.9270109 File: 5 KB, 379x257, PHY_error_analysis1.gif [View same] [iqdb] [saucenao] [google] physics freshman here.If I'm measuring something with a metre stick say to the nearest 1mm, is the error 0.5mm or 1mm? Say I get 169mm, is that 169 + or - 0.5mm, or 169 + or - 1mm?Or say I'm reading off an oscillator the requency and it gives 52.1Hz, is that with an error of 0.1Hz or 0.05Hz?
 >> Anonymous Wed Nov 1 19:19:56 2017 No.9270114 >>9270109measurement error would be 1mm, as that's the lowest level of precision available to you.you could find a statistical error in length by using a number of different rulers and making the same measurement
 >> Anonymous Wed Nov 1 19:22:06 2017 No.9270120 >>9270114thanks anon
 >> Anonymous Wed Nov 1 19:24:06 2017 No.9270123 >>9263958How the FUCK do I do this>A weather channel has the local forecast on the hour and at 10, 25, 30, 45, and 55 minutes past. Suppose you wake up in the middle of the night and turn on the TV. Let X be the time you have to wait until the beginning of the next local forecast, measured in minutes. Find the density function of X.I can see the relative probabilities of 5, 10, and 15 minute waits but I'm stuck
 >> Anonymous Wed Nov 1 19:38:52 2017 No.9270156 Damn, my brain doesn't want to understand how multiplaying two sequences works.For instance, I want to multiply the sequences:( a n ·x n +a n−1 ·x n−1 +...+a 1 ·x+a 0 ) * ( b n ·x n +b n−1 ·x n−1 +...+b 1 ·x+b 0 )How do I write the product of this?
 >> Anonymous Wed Nov 1 19:40:39 2017 No.9270159 >>9270156one element at a time.first element of the first sequence in multiplied by the entire second sequence. then the second element of the first sequence. then the third.
 >> Anonymous Wed Nov 1 19:47:33 2017 No.9270169 >>9270159I see, I'll try my best. Thanks by the way.
 >> Anonymous Wed Nov 1 19:53:10 2017 No.9270179 How do I find a Riemann sum using a TI-84? I store $f(x)=sin(3x)$ as $Y_1$, then I bring up the summation function, but I have no clue how to put in $x_k^*$, and I especially have to idea what to change when I want to find the RRS instead of the LRS.
 >> Anonymous Wed Nov 1 19:58:41 2017 No.9270189 >>9270179In my example, I'm trying to find the LRS, RRS, and MRS on the interval [0,$\pi/2$]. Not asking for answers, I just want to know how to find it.
 >> Anonymous Wed Nov 1 20:04:49 2017 No.9270198 Can someone explain very simply what a group homomorphism is?
 >> Anonymous Wed Nov 1 20:06:39 2017 No.9270199 >>9270198the definition is as clear as it gets, bud.
 >> Anonymous Wed Nov 1 20:14:43 2017 No.9270210 >>9270198>homomorphism>homoit has to do with gays>morphismit has to do with formsso>homomorphismhas to do with gay forms
 >> Anonymous Wed Nov 1 20:21:31 2017 No.9270221 >>9270210I thought it was the engineers who were gay, not the mathematicians.
 >> Anonymous Wed Nov 1 20:30:47 2017 No.9270234 >>9270198Arbitrary functions are terribly behaved, so we just consider ones that play nicely with the structure of groups. It lets you transfer statements about one group to another, basically.
 >> Anonymous Wed Nov 1 20:52:29 2017 No.9270268 >>9270109Perhaps it depends on your professor etc. as I have seen varying answers but I can say with certainty that I was taught that the uncertainties would be $\pm 0.5mm, \pm 0.05Hz$ respectively.
 >> Anonymous Wed Nov 1 21:10:26 2017 No.9270292 >>9270156It's just how you multiply polynomials$c_0 + c_1 x+ \cdots + c_{n+m}x^{n+m}$ , where $c_k = \sum\limits_{i,j:i+j=k} a_i b_j = \sum\limits_{i=0}^{k} a_i b_{k-i}$
 >> Anonymous Wed Nov 1 21:19:10 2017 No.9270302 >>9270198f:G1-->G2 If you perform the operation of G1 on two elements of G1 and then send the result to G2 via f, it is the same as sending the two elements to G2 via f and performing the operation of G2 on their images.
 >> Anonymous Wed Nov 1 21:23:19 2017 No.9270307 Hey /sci/. I'm losing my mind here. There was some way of transforming a fraction with a sum in the denominator into a sum of multiple functions with a single variable in the denominator. I cannot remember the name of this technique for the life of me.$\frac{1}{a+b} = \frac{A}{a} + \frac{B}{b}$It looks something like that. Please give me a name for this thing so I can google it and learn more.
 >> Anonymous Wed Nov 1 21:29:01 2017 No.9270318
 >> Anonymous Wed Nov 1 21:31:33 2017 No.9270325 >>9270198A function from domain G to a codomain G' where f(ab)=f(a)f(b)(a,b are in G)
 >> Anonymous Wed Nov 1 21:36:40 2017 No.9270337 >>9270325What does the word "explanation" mean to you?
 >> Anonymous Wed Nov 1 21:59:39 2017 No.9270372 >>9263958why is my chem professor such a spaz when it comes to VSEPR models ?
 >> Anonymous Wed Nov 1 22:06:55 2017 No.9270388 How can I find the volume of a figure such as x^2+y^2=5z^2 from z=0 to 3 using integrals?I could find it by using the formula V=pi*r*h, but I want to know how to do it using integrals. I think it would be something like $\int_{0}^{3}\int_{-\sqrt{5z^2}}^{\sqrt{5z^2}}\int_{-\sqrt{5z^2-y^2}}^{\sqrt{5z^2-y^2}}dxdydz$, how wrong am I?
 >> Anonymous Wed Nov 1 22:51:46 2017 No.9270435 So I was reading a book about control and got to the PID. But I don't understand the I, how is the integral of the error supposed to cancel the noise, if that's what it is doing?
 >> Anonymous Wed Nov 1 22:59:40 2017 No.9270444 >>9270023so minor update on this, I realized after re-reading the sterno cans they were Sterno "green" made with Ethyl alchohol not methanol....
 >> Anonymous Wed Nov 1 23:11:15 2017 No.9270462 >>9270318Oh thank God thank you, that's exactly it.
 >> Anonymous Wed Nov 1 23:46:10 2017 No.9270511 >>9270198think of a function as a translation. not all translations are good. what's good?multiplying in A, then translating into B is the same as translating operands into B, then multiplying there
 >> Anonymous Thu Nov 2 00:25:13 2017 No.9270566 someone explain to me the subgroup classification of SO(3). And while u are at it, also explain me the symmetries of the polyhedrons.
 >> Anonymous Thu Nov 2 01:36:27 2017 No.9270661 Is it okay to approach a professor (never had a class with) with interest in undergrad research opportunities at this time?(about half way+ through semester) Or is it best to wait until the beginning of a semester?
 >> Anonymous Thu Nov 2 01:44:21 2017 No.9270667 >>9270661Just go dude. It's pretty much the professor's duty to help on such stuff.
 >> Anonymous Thu Nov 2 09:06:19 2017 No.9271073 >>9270661If anything, it would be harder to do it at the beginning of a semester. Just go chat with them about what they're interested in.
 >> Anonymous Thu Nov 2 09:29:44 2017 No.9271106 File: 5 KB, 331x225, integral.png [View same] [iqdb] [saucenao] [google] How did Wolfram get the partial fractions?I did the steps but I got $\frac{x+1}{(x^2+1)^2}$ instead of $/frac {x}{(x^2+1)^2}$
 >> Anonymous Thu Nov 2 09:30:48 2017 No.9271108 >>9271106Oh I fucked up with latex$\frac {x}{(x^2+1)^2}$
 >> Anonymous Thu Nov 2 11:12:38 2017 No.9271279 Is a function sum(s), which takes a string of Natural numbers and outputs the sum of the given numbers, such that sum((1,2,3))=6 for example, surjective?It quite obviously is but how do i structure a proper proof for this?
 >> Anonymous Thu Nov 2 11:17:35 2017 No.9271292 >>9271279>It quite obviously is but how do i structure a proper proof for this?sum((n))=ntherefore surjective
 >> Anonymous Thu Nov 2 11:31:18 2017 No.9271331 >>9271292i just realized how brainlet i really am
 >> Anonymous Thu Nov 2 12:09:41 2017 No.9271405 >>9270388That sounds like masochism to me. It's much simpler to change it into cylindrical coordinates. So let $x = r \cdot cos(\theta)$, $y = r \cdot sin(\theta)$ and $z = z$. The jacobian is just $r$, so the volume element is $dV = r\space dr d\theta dz$. Now the equation is $5 z^2 = r^2 \rightarrow r = \sqrt{5}\space z$, a cone. The limits of integration become[eqn] \int_z \int_\theta \int_r r dr d\theta dz = \int_{z =0}^{z =3} \int_{\theta =0}^{\theta =2\pi} \int_{r=0}^{r=z\sqrt{5}}rdrd\theta dz = 2\pi \int_0^3 \frac{5z^2}{2}dz = 45\pi [/eqn]
 >> Anonymous Thu Nov 2 12:15:47 2017 No.9271412 >>9265461Don't answer those autists, no one cares except those mentally challenged individuals. Nothing we can do about them sadly as autism is incurable.
 >> Anonymous Thu Nov 2 12:36:17 2017 No.9271453 Hey (((faggots))) , new thread>>9271297
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