Question

what do you mean by binomial coefficient ​

Answer 1

Binomial coefficient:

In mathematics, the binomial coefficients are the positive integers that occur as coefficients in the binomial theorem. Commonly, a binomial coefficient is indexed by a pair of integers n ≥ k ≥ 0 and is written $n C_{r}$.

It is the coefficient of the $x^{k}$  term in the polynomial expansion of the binomial power $(1+x)^{k}$, and it is given by the formula

                           $n C_{r}=\frac{(n) !}{(n-r) !(r) !}$