## Prove that value of zero factorial is 1.

Solution : We have, P(n, r) = \(n!\over (n – r)!\) Putting r = n, \(\implies\) P(n, n) = \(n!\over 0!\) \(\implies\) n! = \(n!\over 0!\) [ \(\because\) P(n, n) = n! ] \(\implies\) 0! = \(n!\over n!\) = 1 Hence, Proved.