Simplify -x square root of 5y^4

$- x \sqrt{5 y^{4}}$

Rewrite $5 y^{4}$ as ${(y^{2})}^{2} \cdot 5$ .

Rewrite $y^{4}$ as ${(y^{2})}^{2}$ .

$- x \sqrt{5 {(y^{2})}^{2}}$

Reorder $5$ and ${(y^{2})}^{2}$ .

$- x \sqrt{{(y^{2})}^{2} \cdot 5}$

Pull terms out from under the radical.

$- x y^{2} \sqrt{5}$