#### Answer

$$5x\sqrt 2$$

#### Work Step by Step

We can use the product rule for square roots to rewrite the two radicals as a single radical, a product of the two radicands:
$$(\sqrt 5x)(\sqrt 10x) = \sqrt (5x\times10x)$$
We multiply the factors in the radicand to get:
$$\sqrt 50x^2$$
$50x^2$ is the product of the perfect square $25x^2$ and $2$.
$$\sqrt(50x^2) = \sqrt (25x^2) \sqrt 2$$
Since $25x^2$ is a perfect square, we can simplify this radical by taking the square root of $25x^2$, which is $5x$:
$$5x\sqrt 2$$