Show by direct calculation that Eqs. (4-134) and (4-137) in the textbook by Duderstadt and Hamilton hold, i.e.:(a) ∫ dΩΩiΩj= 4π/3 δij; i,j = x,y,z;
4π(b) ∫ dΩΩxΩyΩz = 0, if l, m, or n is odd.
4π
The integrals are over 4π.
This is part of the derivation of the diffusion equation...