Incorrect. Start with: $\displaystyle\sqrt{{-{40}}}=\sqrt{{{40}\cdot{\left(-{1}\right)}}}\usepackage{cmbright}\Huge\$

Use the rule $\displaystyle\sqrt{{{a}{b}}}=\sqrt{{{a}}}\sqrt{{{b}}}\usepackage{cmbright}\Huge\$ and the definition $\displaystyle{i}=\sqrt{{-{1}}}\usepackage{cmbright}\Huge\$ to simplify.