Answer:
[tex]\large\boxed{\sqrt{20}-\sqrt{80}=-2\sqrt5}[/tex]
Step-by-step explanation:
[tex]\text{Use}\ \sqrt{ab}=\sqrt{a}\cdot\sqrt{b}\\\\\sqrt{20}=\sqrt{4\cdot5}=\sqrt4\cdot\sqrt5=2\sqrt5\\\\\sqrt{80}=\sqrt{16\cdot5}=\sqrt{16}\cdot\sqrt5=4\sqrt5\\\\\sqrt{20}-\sqrt{80}=2\sqrt5-4\sqrt5=(2-4)\sqrt5=-2\sqrt5[/tex]
