Recent content by chredhat

let m,n be positive integer. Prove the identity: sum (i from 0 to k): { C(m, i) * C(n, k - i) } = C(m + n, k) Hint: Consider the polynomial equation: sum (k from 0 to m+n) {C(m + n, k) *z^k } = (1 + z)^(m+n) = ((1+z)^m) * ((1+z)^n) I tried long time, still have no idea.