I have the function\fourier series
$$ f(x) = \frac{1}{4} + \sum_{i=0}^\infty \frac{1}{3^k}\cos(2kx) $$
and I am asked to compute the integral
$ \int_{0}^\pi f(x)^2 dx$
How do I proceed? I think I should use Parseval's identity, but my attempts failed, and I don't know how the fact that the period is $\pi$ might affect the calculation
Thanks!