## Introductory Algebra for College Students (7th Edition)

$10x$
Using $\sqrt{x}\cdot\sqrt{y}=\sqrt{xy}$ or the product rule of radicals, the given expression, $\sqrt{20x}\cdot\sqrt{5x} ,$ is equivalent to \begin{array}{l}\require{cancel} \sqrt{20x(5x)} \\\\= \sqrt{100x^2} \\\\= \sqrt{(10x)^2} \\\\= 10x .\end{array} Note that variables are assumed to have positive real numbers.