Question

Reduce the following PDE to a set of three ODEs by the method of separation of variables. d^2u/dr^2 +(2/r)(du/dr)+(1/r^2)(d^2u/dθ ^2) +(cot θ/r^2)(du/dθ) + (1/r^2 sin^2 θ)(d^2u/d φ^2) =0