discrete mathematics - Show the closed form of the sum $sum_{i=0}^{n-1} i x^i$

Can anybody help me to show that when $x\neq 1$

$$\large \sum_{i=0}^{n-1} i\, x^i = \frac{1-n\, x^{n-1}+(n-1)\,x^n}{(1-x)^2}$$