Answer
$-\dfrac{1}{9}$
Work Step by Step
Using the concepts of radicals, the given expression, $
-\dfrac{1}{\sqrt{81}}
,$ is equivalent to
\begin{align*}\require{cancel}
&
-\dfrac{1}{\sqrt{9^2}}
\\\\&=
-\dfrac{1}{9}
.\end{align*}
Hence, the given equation simplifies to $
-\dfrac{1}{9}
.$
