# Finding particular solution with fourier series

1. Jan 23, 2009

### naggy

I was wondering what to do if I have a DE like this

$$x'' + \omega^2x = \cos^2(t) \sin^2(t)$$

I have to decide for what omega it has a solution with period 2pi.

Now to solve this I have to find the fourier series representation of the right hand side, but the problem is that I get all An = Bn = 0 ??

2. Jan 23, 2009

### naggy

wait! The right hand side already is a fourier series