Compute the coefficients $ a_k $ of the Fourier series of the signal x(t) periodic with period T = 4 defined by
$ \,x(t)=\left\{\begin{array}{cc} 0, & -2<t<-1 \\ 1, & -1\leq t\leq 1 \\ 0, & 1<t\leq 2 \end{array} \right. \, $
$ T = \frac{2\pi}{w_0} = 4 $
$ w_0 = \frac{\pi}{2} $
