Fourier series

The Fourier series expansion of x 3 in the interval −1 ≤ x < 1 with periodic continuation has

The Fourier cosine series for an even function $f(x)$ is given by $f(x) = a_0 + \sum_{n=1}^{\infty} a_n \cos(nx)$. The value of the coefficient $a_2$ for the function $f(x) = \cos^...