Finding a2 in a Fourier Series

[andre_1]

Homework Statement

Find the term a2 in the following Fourier seies:


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

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!

 

[HallsofIvy]

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?