# How do you simplify sqrt(45x^3) - sqrt(20x^3)?

$x \sqrt{5 x}$
Since we have $x \ge 0$ we can write
$\sqrt{9 {x}^{2} \cdot 5 \cdot x} - \sqrt{4 \cdot {x}^{2} \cdot 5 \cdot x} = 3 x \sqrt{5 x} - 2 x \sqrt{5 x} = x \sqrt{5 x}$