A formula that expresses the sum of certain binomial coefficients as a single binomial coefficient. It is written as (m+n choose k) = ∑[r=0 to k] (m choose r) (n choose k-r).
A formula that expresses the sum of certain binomial coefficients as a single binomial coefficient. It is written as (m+n choose k) = ∑[r=0 to k] (m choose r) (n choose k-r).