It appears that you multiplied the radicands, ignoring the radical signs. The correct value of the given expression is $\displaystyle{2}{\sqrt[{{3}}]{{{8}{{x}}^{{6}}{{y}}^{{2}}}}}\usepackage{cmbright}\Huge\$ . Rewrite factors of the radicand as perfect cubes, then rewrite the radical as the product of three factors. Simplify cube roots of perfect cubes.