[EQ] \begin{align} \frac{1}{(1-x)^2} + \frac{2x}{(1-x)^3} &= \sum_{n=0}^\infty n^2x^{n-1}\\ &\Leftrightarrow\\ \frac{1-x}{(1-x)^3} + \frac{2x}{(1-x)^3} &= \sum_{n=0}^\infty n^2x^{n-1}\\ &\Leftrightarrow\\ \frac{1+x}{(1-x)^3} &= \sum_{n=0}^\infty n^2x^{n-1} \end{align} [/EQ]