The greatest positive integer which divides n(n+1)(n+2)…(n+r−1)∀n∈N is
Prove that: (i) n!(n−r)! = n(n-1)(n-2)...(n-(r-1)) (ii) n!(n−r)!r!+n!(n−r+1)!(r−1)! = (n+1)!r!(n−r+1)!