So I know that I need to get this into the form 1/(1-n), but I don't know how...
Please show. Thanks.
Surely, you know that $\displaystyle e^z=\sum_{n=0}^\infty\frac{1}{n!}z^n$, and thus you have $\displaystyle e^{-z}=\sum_{n=0}^\infty\frac{1}{n!}(-z)^n=\sum_{n=0}^\infty \frac{(-1)^n}{n!}z^n$