Im having difficulty with D.T. Fourier Transforms
$ \chi(\omega) = F(x[n]) = \sum_{n=-\infty}^\infty x[n]e^{-j\omega n} $
$ x[n] = \frac{1}{2\pi} \int_{2\pi} \chi(e^{j\omega})e^{j\omega n} d\omega $
