Compute $\displaystyle \sum_{0}^{\infty}(n^{2}+n)x^{n}$ for fixed values of x.

I know this sum is infinity when $\displaystyle \left|x \right|\geq1$, but how do you compute the value of the sum explicitly when $\displaystyle \left|x \right|<1$? The best I can seem to do is to use the Gaussian formula for the sum of the first n integers to deal with the $\displaystyle (n^{2}+n)$ term. Any suggestions?