Question

8. Prove that:
(i) n!/ r! = n(n − 1)(n − 2) ... (r + 1)​

Answer 1

Answer:

$\frac{n!}{r!} = \frac{1.2.3...(r - 1)r(r + 1)....(n - 1)n}{1.2.3.....(r - 1)r} \\ \\ = {(r + 1)}(r + 2).....(n - 2)(n - 1)n \\ \\ = n(n - 1)(n - 2)....(r + 1) \\ \\ note \: \: its \: \: only \: \: true \: \: if \: n \geqslant r$

Answer 2

Answer:

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