Question

Prove that:


n!/(n-r)! = n(n-1) (n - 2)... (n - (r - 1))




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Answer 1

Answer:

Solution :

We have

n(n−1)(n−2)...(n−r+1)

=n(n−1)(n−2)...(n−r+1).(n−r)!(n−r)!

[ multiplying num. and denom. by (n−r)!]

=n!(n−r)!.

Hence, n(n−1)(n−2)...(n−r+1)=n!(n−r)!.