Calculus

In the Fourier series expansion of the function $f(x) = x^2$ on the symmetric interval $[-\pi, \pi]$, calculate the constant term $a_0 = \frac{1}{\pi} \int_{-\pi}^\pi x^2 dx$. (Express as a multiple of $\pi^2$, i.e. $a_0 / \pi^2$).