Question

Find the coefficient of x^5 in (1+x)^11.

Answer 1

$\text{According to the binomial theorem}$

$(1+x)^n= \displaystyle\sum_{k=0}^{n} \binom{n}{k}x^k$

$\text{coefficient of }x^5 \ \binom{11}{5}=\frac{11!}{5!6!}=462$

Answer: 462