Answer
$6x$
Work Step by Step
Using $\sqrt{x}\cdot\sqrt{y}=\sqrt{xy}$ or the product rule of radicals, the given expression, $
\sqrt{12x}\cdot\sqrt{3x}
,$ is equivalent to
\begin{array}{l}\require{cancel}
\sqrt{12x(3x)}
\\\\=
\sqrt{36x^2}
\\\\=
\sqrt{(6x)^2}
\\\\=
6x
.\end{array}
Note that variables are assumed to have positive real numbers.
