equation icon  x(1 - x)pin''+ [1 - s- ie - it - (2- 2it)x]pin'+ [it(1 - it) + n(n + 1)]pin = ' 2iek[- x(1 - x)pin + (1 - s + ie- it)xpin] +[n(n + 1) - c - s(s + 1) + e2 - iek(1 - 2s)]pin. (119)