n=0 Multiplying this equation by -2Rr, multiplying the expression for 1/1 by -R, and then adding the two equations yields R(r2 - R2 ) R n+1 13 (2n + 1) Pn(cos ?) . (1-122) n=0 The right-hand side is the bracketed expression in (1-119). Substituting the left-hand side, we finally obtain Ve(r, v, 1) = R(r2 - R2 V(R, d', X') sin o' do'dx' , (1-123) 4TT X' =0Jo=0 73 where l= vr2+ R2 - 2Rr cosy. (1-124)