Am really not sure how to prove this question, does

$\displaystyle \nabla . (\frac{1}{r}r) $= $\displaystyle \frac{\partial}{\partial x} + \frac{\partial}{\partial y} + \frac{\partial}{\partial z} \dot $ (\frac{1}{x^{2}+y^{2}+z^{2})^{1/2} ( x+y+z) [/tex]