物理

交友贴......

$\frac{(-1)^n}{n}$

$\frac{1}{\sqrt{n^2+1}}+\frac{1}{\sqrt{n^2+2}}+\cdots+\frac{1}{\sqrt{n^2+n}}$

$\overrightarrow{E(\vec{r})}$

$\iint\limits_D\dfrac{\partial Q}{\partial X}{\rm d}x$

这有着细微差别

$\iint\limits_D\left(\dfrac{\partial Q}{\partial X}-\dfrac{\partial P}{\partial Y}\right){\rm{dx}}{\rm{dy}}$