Answer
$11a^{45}$
Work Step by Step
Extracting the factors that are perfect powers of the index, the given expression, $
\sqrt{121a^{90}}
,$ is equivalent to
\begin{align*}\require{cancel}
&
\sqrt{(11a^{45})^2}
\\\\&=
11a^{45}
.\end{align*}
Hence, the given expression simplifies to $
11a^{45}
$.
