[tex]-2\sqrt{20}-\sqrt{125}=-2\sqrt{4\cdot5}-\sqrt{25\cdot5}\\\\\text{use}\ \sqrt{ab}=\sqrt{a}\cdot\sqrt{b}\ \text{for}\ a\geq0\ \wedge\ b\geq0\\\\=-2\sqrt4\cdot\sqrt5-\sqrt{25}\cdot\sqrt5=-2(2)\sqrt5-5\sqrt5\\\\=-4\sqrt5-5\sqrt5=(-4-5)\sqrt5=\boxed{-9\sqrt5}[/tex]
