# How do you simplify 5sqrt80?

$5 \sqrt{80} = 20 \sqrt{5}$
$5 \sqrt{80} = 5 \sqrt{{4}^{2} \cdot 5} = 5 \sqrt{{4}^{2}} \sqrt{5} = 5 \cdot 4 \sqrt{5} = 20 \sqrt{5}$
using identity $\sqrt{a b} = \sqrt{a} \sqrt{b}$ (when $a \ge 0$ and $b \ge 0$).