Answer
$72$
Work Step by Step
Using $P(n,r)=\dfrac{n!}{(n-r)!},$ the given expression, $P(
9,2
),$ evaluates to
\begin{array}{l}\require{cancel}
=\dfrac{9!}{(9-2)!}
\\\\=
\dfrac{9!}{7!}
\\\\=
\dfrac{9(8)(7!)}{7!}
\\\\=
\dfrac{9(8)(\cancel{7!})}{\cancel{7!}}
\\\\=
72
\end{array}