Javier
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 Nov 9 comment Understanding linear vector subspaces If "linear subspace" means subspace of a vector space, then I.2 and II.2 aren't subspaces. Nov 9 comment Simultaneous equation other possibilities but how? ($14x - 5y + 14 = 179, \ -14x + 5y + 5 = -160$) I'm sorry if there's something I'm not getting, but couldn't you just set $x=15$, for example, and solve for $y$?. It's not like $(15,9)$ is the only solution, even if you just consider integers, so I don't see how can it be the answer. Nov 9 comment Simultaneous equation other possibilities but how? ($14x - 5y + 14 = 179, \ -14x + 5y + 5 = -160$) Why do you decide that you only want integers? I don't see that in the question. Nov 8 answered Simultaneous equation other possibilities but how? ($14x - 5y + 14 = 179, \ -14x + 5y + 5 = -160$) Nov 8 comment Simultaneous equation other possibilities but how? ($14x - 5y + 14 = 179, \ -14x + 5y + 5 = -160$) I don't know how you got $y=1$, but your problem is those two equations are actually the same. This means that you will have infinite solutions. Nov 7 comment Solve complex equation. Try using polar form ($z = re^{i\theta}$). Nov 6 comment Telling where a function is differentiable $C^1$ implies differentiability as far as I remember. That is, continuity of both partial derivatives suffices to prove that a function is differentiable (existence isn't enough). However, with some functions (like your second one) it can be easier to just check the definition of differentiability than to actually differentiate and check continuity. Nov 5 answered Prove $\forall K > 0: \lim_{n\rightarrow\infty} \sqrt[n]{K} = 1$ Nov 5 comment Solve $2a + 5b = 20$ Anyway, I don't understand the thinking process. How do you get from $2a+5b =20$ to $0a+5b=20$? That's certainly not a valid step. Nov 5 comment Solve $2a + 5b = 20$ Are $a$ and $b$ supposed to be integers or real numbers? I don't really know a lot about number theory, but I know that if they're real numbers then there are infinite solutions. Nov 4 accepted Proving statement about dimensions of vector spaces Nov 2 comment Multivariable Limits @Arjang: It can be defined with the same $\epsilon$-$\delta$ definition used for single variable limits. Nov 1 comment Multivariable Limits @Arjang: are you sure about that? Take $\frac{xy}{x^2+y^2}$; if you compute the limit with $x$ first and then $y$ or with $y$ first and then $x$ it gives $0$ both times, but the limit doesn't exist (take the line $y=x$). Nov 1 comment Proving the existence of a point $a \in \mathbb{R}_+$ s.t. $\cos(a) < 0$ Nitpick: your second property should be $\cos x = \Re(\exp(ix))$. Oct 30 comment Finding $\nabla f$ of given implicit fuction. What have you tried so far? Oct 30 comment Equation of sine wave around a circle @Matthew: assuming we're interpreting the quedtion correctly, wouldn't it be $\sin 4\theta$? Oct 24 awarded Yearling Oct 24 comment Need help differentiating this equations I'm guessing it should be $R (\hat z \cdot R)$. Oct 16 answered Fourier series for $\sin x$ is zero? Oct 16 comment Fourier series for $\sin x$ is zero? But for $n=1$ you need to integrate $\sin^2 x$.