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 Feb 12 asked Solving a delay differential equation Feb 11 comment Why do you need absolute value when taking $\sqrt{\cos^2(x)}$ $\sqrt{\cos^2(x)}\neq\cos(x)$ for all $x$. Feb 10 revised Is it true that $|e^z|\le e^{|z|}$ for all $z \in \mathbb C$? added 53 characters in body Feb 10 answered Is it true that $|e^z|\le e^{|z|}$ for all $z \in \mathbb C$? Feb 10 answered Product of terms involving complex exponents Feb 10 comment Prove that for any integer $n$, if $b^2$ divides $n$, then $b$ divides $n$. $$b^2\mid n\implies n=b^2k=bbk=b\ell\implies b\mid n.$$ Feb 9 comment Proving that $\binom{n}{k}\binom{\smash{k}}{m}\binom{m}{r} = \binom{n}{r}\binom{n-r}{n-m}\binom{n-m}{n-k}$ Use the definition of the Binomial coefficient. Feb 3 revised Compute the integrals using the residue theorem added 4 characters in body Feb 3 answered Compute the integrals using the residue theorem Jan 31 comment Finding the value of this integral $\int_{-\pi/4}^{\pi/4}{ (\cos{t} + \sqrt{1 + t^2} }\sin^3{t}\cos^3 {t})dt$? Very nifty !... Jan 31 comment Finding the value of this integral $\int_{-\pi/4}^{\pi/4}{ (\cos{t} + \sqrt{1 + t^2} }\sin^3{t}\cos^3 {t})dt$? You could split the integral into two terms. The first term should be easy to integrate. For the second, you may find $\frac{1}{2}\sin(2t)=\sin(t)\cos(t)$ useful. Jan 30 comment why $\int{\cos({\pi}t)} dt = \frac{1}{\pi}\sin({\pi}t)$? When something new is "added" we can assume the old rules will work, but often they don't work meaning there's more going on than we know. One way to think is to always remember that the rules we know at present are some special case of more general rules. So e.g. your statement $\int\cos(x)dx=\sin(x)+C$ is a special way of writing $\int\cos(1\cdot x)=\sin(x)+C$, but what if the $1$ were some other number $a$. What general rule is there to handle such cases? It's not as straight forward as the case when $a=1$. Jan 27 comment Prove convergence of $\sum _{n=1}^{\infty }\sin(1/n)/n$ Since $1/n\to 0$ as $n\to\infty$, maybe you could consider $\sin(1/n)$ in a neighbourhood of $0$, e.g. $\sin(1/n)\to1/n$ as $n\to\infty$... Jan 22 awarded Yearling Jan 22 comment Finding the result of an infinite sum That's no reason to methodically downvote every element of a question though. Jan 20 revised I need to solve $\phi (x,y) = \frac{2V}{\pi} \int_{0}^{\infty} \frac{\sin(kx)\cosh(ky) dk}{k\cosh(ka)}$ added 763 characters in body Jan 19 answered I need to solve $\phi (x,y) = \frac{2V}{\pi} \int_{0}^{\infty} \frac{\sin(kx)\cosh(ky) dk}{k\cosh(ka)}$ Jan 19 revised I need to solve $\phi (x,y) = \frac{2V}{\pi} \int_{0}^{\infty} \frac{\sin(kx)\cosh(ky) dk}{k\cosh(ka)}$ added 2 characters in body Jan 19 revised I need to solve $\phi (x,y) = \frac{2V}{\pi} \int_{0}^{\infty} \frac{\sin(kx)\cosh(ky) dk}{k\cosh(ka)}$ added 2 characters in body Jan 19 comment Name for “3D quadrilateral” shape? Thank you Andrew. I will have a think about your comment.