Boundary Values & Fourier Series · Easy problem

Find the coefficient $a_2$ of $\cos 2x$ in the Fourier series on $[-\pi, \pi]$ of $f(x) = x^3 + 4\cos 2x$, where $a_n = \dfrac1\pi\displaystyle\int_{-\pi}^{\pi} f(x)\cos nx\,dx$.