A solid insulating sphere of radius R has a nonuniform charge density that varies with r according to the expression `rho = Ar^2`, where A is a constant and rltR is measured from the centre of the sphere. Show that (a) the magnitude of the electric field outside (rgtR) the sphere is `E = AR^5//5epsilon_0r^2` and (b) the magnitude of the electric field inside (rltR) the sphere is `E = AR^3//5epsilon_0`.