## Thinking Mathematically (6th Edition)

$9\sqrt{2}$
Factor each radicand so that one of the factors is a perfect square: $=\sqrt{25(2)} + \sqrt{16(2)} \\=\sqrt{5^2(2)} + \sqrt{4^2(2)}$ Simplify each radical to obtain: $=5\sqrt{2} + 4\sqrt{2}$ Combine like terms to obtain: $=(5+4)\sqrt{2} \\=9\sqrt{2}$