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)

$n + 1$

Answer 2

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