Question

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

• A. $\frac{2^n}{2!}$
• B. $n+1$
• C. $n$
• D. $2n$

Answer 1

Answer: (B)

$\because {\left(1-x\right)}^{-2}=1+2x+3x^2+...+\left(n+1\right)x^n+...$
$\therefore$ Coefficient of $x^n=n+1$