## Precalculus: Concepts Through Functions, A Unit Circle Approach to Trigonometry (3rd Edition)

$P(8,8) = 40,320$
Use the formula $P=\dfrac{n!}{(n-r)!}$ to obtain: $\require{cancel} P(8,8) \\=\dfrac{8!}{(8-8)!} \\=\dfrac{8(7)(6)(5)(4)(3)(2)(1)}{0!} \\=\dfrac{40,320}{1} \\=40,320$ We find here that when $n=r$, $P(n,r) = n!$.