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Question Number 150554 by pete last updated on 13/Aug/21

Show that n_{C_{r}} = \frac{n (n - 1) (n - 2) \dots (n - r + 1)}{r!}

Answered by Ar Brandon last updated on 13/Aug/21

\frac{n (n - 1) (n - 2) \dots (n - r + 1)}{r!}

= \frac{n (n - 1) \dots (n - r + 1) (n - r)!}{(n - r)! r!}

= \frac{n!}{(n - r)! r!} = \overset{n}{} C_{r}

Commented by pete last updated on 15/Aug/21

Thank you sir

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