Chapter 8 - Section 8.2 - Multiplying and Dividing Radicals - Exercise Set - Page 585: 19

$10\sqrt{2}$

Getting the perfect factors and then extracting its root, the simplified form of the given expression, $ \sqrt{200} ,$ is \begin{array}{l}\require{cancel} \sqrt{100\cdot2} \\\\= \sqrt{(10)^2\cdot2} \\\\= 10\sqrt{2} .\end{array}