Answer
$-3\sqrt 5$
Work Step by Step
To simplify the expression, we will simplify the term within the square root by writing it as its two constituent factors:
$-\sqrt {45}$
=$-\sqrt {9\times5}$
=$-(\sqrt 9\times\sqrt 5)$
=$-(\sqrt {3^{2}}\times\sqrt 5)$
=$-(3\times\sqrt 5)$
=$-3\sqrt 5$
