- 10

- 0

\begin{align*}

\frac{\partial}{\partial r_k}\frac{\partial}{\partial r_m}=\frac{3r_k r_m - r^2 \delta_{km}}{r^5}-\frac{4\pi}{3}\delta_{km}\delta(\mathbf{r})\\

\end{align*}

I am having trouble with figuring out how to show this identity is true. If anyone can help get me on the right track to see how to achieve this identity I would greatly appreciate it.