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

$C(15,15) = 1$
We know, $C(n,r) = \dfrac{n!}{(n-r)!r!}$ In this case, $C(15,15) \\= \dfrac{15!}{(15-15)!\times15!} \\= \dfrac{15!}{0!\times15!} \\=\dfrac{15!}{15!} \\=1$