You may have correctly separated the factors into perfect squares and then taken the square roots of each. However, you left out the factor $\displaystyle\sqrt{{{y}}}\usepackage{cmbright}\Huge\$ when multiplying and simplifying. You also forgot the rule that $\displaystyle\sqrt{{{{x}}^{{2}}}}={\left|{x}\right|}\usepackage{cmbright}\Huge\$ .