I presume you mean rather than "e"!

Certainly you should have no trouble putting and into spherical coordinates (isa sphere with radius a. So I assume the problem is . It's not really hard to put the formulas for x, y, and z, in terms of , , and and reduce but I think I would be inclined to add a to each side to get . Now the left side is and the right side is, as I said before, very easy.