# How do you simplify 4sqrt5-2sqrt45?

I found: $- 2 \sqrt{5}$
$4 \sqrt{5} - 2 \sqrt{5 \cdot 9} =$
$= 4 \sqrt{5} - 2 \cdot 3 \sqrt{5} =$
$= 4 \sqrt{5} - 6 \sqrt{5} = - 2 \sqrt{5}$