Question Number 87682 by john santu last updated on 05/Apr/20
$$\mathrm{what}\:\mathrm{is}\:\bigtriangledown^{\mathrm{2}} \left(\frac{\mathrm{1}}{\overset{\rightarrow} {\mathrm{r}}}\right)\:\mathrm{if}\: \\ $$$$\overset{\rightarrow} {\bigtriangledown}\:=\:\hat {\mathrm{i}}\:\frac{\partial}{\partial\mathrm{x}}+\hat {\mathrm{j}}\frac{\partial}{\partial\mathrm{y}}+\hat {\mathrm{k}}\:\frac{\partial}{\partial\mathrm{z}} \\ $$$$\mathrm{and}\:\overset{\rightarrow} {\mathrm{r}}\:=\:\hat {\mathrm{i}x}\:+\:\hat {\mathrm{j}y}\:+\:\hat {\mathrm{k}z}\: \\ $$