Chapter 9 - Roots and Radicals - 9.2 - Simplifying Radicals - Problem Set 9.2 - Page 406: 8

$3 \sqrt{10}$

In order to simplify a radical, we consider the factors of the number inside of the radical. If any of these factors are perfect squares, meaning that their square root is a whole number, then we can simplify the radical. We know that 9 and 10 are factors of 90. We know that 9 is a perfect square, so we simplify: $ \sqrt{9} \sqrt{10}=3 \sqrt{10}$