# Fourier Series

1. Nov 13, 2007

### andre_1

1. The problem statement, all variables and given/known data

Find the term a2 in the following fourier seies:

[4+5 (cos x )^2]^(1/2) dx= ao + a2 cos (2x) + a4 cos (4x)

3. The attempt at a solution
The only thing I can think about is transforming that to complex numbers but I am not completely sure...

I know that a0 is supposed to be 3.966360

Thanks!

2. Nov 14, 2007

### HallsofIvy

Staff Emeritus
Is that an integral on the left side? Are you asked to write
$$\int\sqrt{4+ 5 cos^2(x)} dx$$
as a Fourier series?