Electrostatic potential — UPSC CSE 2019 Physics PYQ

Starting from the expression for the electrostatic potential \phi(\vec{r})=\frac{1}{4\pi\varepsilon_0}\int_V\frac{\rho(\vec{r}_0)}{|\vec{r}-\vec{r}_0|}\,dV_0 obtain Poisson's equation \nabla^2\phi=-\frac{\rho}{\varepsilon_0}. [Symbols have their usual meanings]