Chapter 8 - Section 8.2 - Multiplying and Dividing Radicals - Exercise Set - Page 585: 6

$10$

Using $\sqrt{x}\cdot\sqrt{y}=\sqrt{xy}$ or the product rule of radicals, the given expression, $ \sqrt{10}\cdot\sqrt{10} ,$ is equivalent to \begin{array}{l}\require{cancel} \sqrt{10(10)} \\\\= \sqrt{(10)^2} \\\\= 10 .\end{array}