Given the Fourier series:
$$F(x)=\sin{x}+\sum_{n=1}^\infty \frac{1}{5^n} \cos{nx}$$
How do I find $a_0, a_1, a_2$ when $$a_0=\frac{1}{\pi} \int_{-\pi}^\pi f(x) dx$$ and $$a_n=\frac{1}{\pi} \int_{-\pi}^\pi f(x) \cos{n x} dx$$
? Also, what is f(x) in this case?
I'm aware that this is a basic question, but I simply can't make sense of this for some reason.