Hi guys I am having difficulty while revising..

Consider the function r=(x^2+y^2+z^2) and f=r^-1

Find Partial derivatives rx,ry,rz. I have done this part but having difficulty doing this part

Use chain rule to find fx,fy,fz and hence show that grad ∆f =(-r^-3)(r) where r=xi+yj+zk