I was just reviewing my class notes and i just cant understand how i solved my problems via general method.....i know and understand this method very well, but i just have missed something,that i cane even understand my own notes for a couple of alike problems.....

problem: (D^2 + a^2)y = sec(aX)

to be solved via general method of differential equations..

now there comes somewhere

P.I=sec(aX)/(D^2+a^2)

= sec(aX)/(D-ia)(D+ia) <<<<--------------------- what is this??

{i =iota}

or if anyone knows anyother way to solve it by general method,...please do help

thanks already