Question

The coefficient of ${{x}^{r}}$ in the expansion of ${{(1-x)}^{-2}}$ is

• A. $r$
• B. $r+1$
• C. $r+3$
• D. $r-1$

Answer 1

Answer: (B)

$r+1$

Answer 2

Since, ${{(1-x)}^{-2}}=1+2x+3{{x}^{2}}+....+(r+1){{x}^{r}}$ $\therefore$
Coefficient of ${{x}^{r}}$ in ${{(1-x)}^{-2}}$ is $(r+1)$ .