For the position vector r = ix+jy+kz, show that div(r/r^3) = 0 (i ∂/∂x + j ∂/∂y + k ∂/∂z) . ( ix + jy + kz/r^3) ∂/∂x(x/r^3) + ∂/∂y(y/r^3) + ∂/∂z(z/r^3) so 1/r^3 + 1/r^3 + 1/r^3. But my coursebook depicts the differentiation as 1/r^3 + x(-3r^-4∂r/∂x) for the first term. Like wise they have used the x^n = nx^n-1 formula for differentiating r^3 in ∂/∂y and ∂/∂z terms too. Revered Members, I am confused. It is partial differentiation with respect to x, then whey should differentiate r by using the power formula. Any help in this regard will be highly appreciated.