Answer
$-(r-2)(r-9)$
Work Step by Step
The given expression, $
-r^2+11r-18
,$ is equivalent to
\begin{align*}
-(r^2-11r+18)
\end{align*}
Using the factoring of trinomials in the form $x^2+bx+c,$ the $\text{
expression
}$
\begin{align*}
-(r^2-11r+18)
\end{align*} has $c=
18
$ and $b=
-11
.$
The two numbers with a product of $c$ and a sum of $b$ are $\left\{
-2,-9
\right\}.$ Using these two numbers, the factored form of the $\text{
expression
}$ above is
\begin{align*}
&
-(r-2)(r-9)
\end{align*}