# How do you simplify sqrt(-81x^6)?

Remember $\sqrt{a \cdot b} = \sqrt{a} \cdot \sqrt{b}$
$= \sqrt{- 1 \cdot {9}^{2} \cdot {\left({x}^{3}\right)}^{2}}$
$= \sqrt{- 1} \cdot \sqrt{{9}^{2}} \cdot \sqrt{{\left({x}^{3}\right)}^{2}}$
$= i \cdot 9 \cdot {x}^{3} = 9 {x}^{3} i$