Elementary Algebra

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