# User

 May 4 comment Why doesn't $\lim_{(x,y)\rightarrow(0,0)} xy\sin(\frac{1}{xy})$ exist?How to know when it's ok to take such $z$? or polar coordinates? May 4 accepted Why doesn't $\lim_{(x,y)\rightarrow(0,0)} xy\sin(\frac{1}{xy})$ exist? May 4 asked Why doesn't $\lim_{(x,y)\rightarrow(0,0)} xy\sin(\frac{1}{xy})$ exist? Apr 30 awarded Custodian Apr 30 revised Find all functions $F(x,y)$ such as $\frac{\sqrt{3}}{2}\frac{\partial{f}}{\partial{x}}+\frac{1}{2}\frac{\partial{f}}{\partial{y}}=0$added 8 characters in body; edited title Apr 30 reviewed Approve suggested edit on Find all functions $F(x,y)$ such as $\frac{\sqrt{3}}{2}\frac{\partial{f}}{\partial{x}}+\frac{1}{2}\frac{\partial{f}}{\partial{y}}=0$ Apr 30 asked Find all functions $F(x,y)$ such as $\frac{\sqrt{3}}{2}\frac{\partial{f}}{\partial{x}}+\frac{1}{2}\frac{\partial{f}}{\partial{y}}=0$ Apr 17 comment How to integrate a vector function in spherical coordinates?Thanks! much clearer now Apr 17 accepted How to integrate a vector function in spherical coordinates? Apr 17 awarded Commentator Apr 17 comment How to integrate a vector function in spherical coordinates?How would you express $\hat{r}$ without converting back to cartesian coordinates? Apr 17 comment How to integrate a vector function in spherical coordinates?But each coordinate should be independent on the other? no? Apr 16 asked How to integrate a vector function in spherical coordinates? Mar 14 awarded Supporter Mar 10 awarded Notable Question Mar 1 comment Let $T$ be a Hermitian operator and $\|v\|=1$, prove $\langle T^2(v),v\rangle \ge\langle T(v),v\rangle^2$I removed the hint from the question, thanks Mar 1 revised Let $T$ be a Hermitian operator and $\|v\|=1$, prove $\langle T^2(v),v\rangle \ge\langle T(v),v\rangle^2$hint was wrong... Mar 1 comment Let $T$ be a Hermitian operator and $\|v\|=1$, prove $\langle T^2(v),v\rangle \ge\langle T(v),v\rangle^2$Oh well... after reading your answer I was under the impression that the hint is wrong. I received it in a test :( Mar 1 comment Let $T$ be a Hermitian operator and $\|v\|=1$, prove $\langle T^2(v),v\rangle \ge\langle T(v),v\rangle^2$I finally understand it, I accepted your answer. I would still like to know how to prove/use the hint Mar 1 accepted Let $T$ be a Hermitian operator and $\|v\|=1$, prove $\langle T^2(v),v\rangle \ge\langle T(v),v\rangle^2$