# How come square root of 18 is 3*square root of 2?

You can write that $18 = 2 \cdot 3 \cdot 3$, so
$\sqrt{18} = \sqrt{2 \cdot 3 \cdot 3} = \sqrt{9 \cdot 2} = \sqrt{9} \cdot \sqrt{2} = 3 \cdot \sqrt{2}$