For a particular n, 
. Therefore we can write the general solution as
, where Cns are yet to be determined.
Given that 
. Therefore 
. Multiplying both sides by 
on both sides and integrating from z =0 to z = d we can write,
.....................(2.129)
Using orthogonality conditions and evaluating the integrals we can show that
..................................................(2.130)