i need help evaluating this: $\displaystyle \sum_{n=0}^\infty \frac{1}{2}^n {e^{-jw(n+1)}}$ i know the answer is: $\displaystyle {e^{-jw}}\frac{1}{1 - \frac{1}{2}e^{-jw}}$ however, im not quite sure how to get to it. I can kind of see how I could evaluate it, but is there a more general way to solve these?