Correct. Use the rule $\displaystyle\sqrt{{{a}{b}}}=\sqrt{{{a}}}\sqrt{{{b}}}\usepackage{cmbright}\Huge\$ and the definition of i.

$\displaystyle\sqrt{{-{40}}}=\sqrt{{{40}\cdot{\left(-{1}\right)}}}=\sqrt{{{40}}}\sqrt{{-{1}}}=\sqrt{{{4}\cdot{10}}}\sqrt{{-{1}}}=\sqrt{{{4}}}\sqrt{{{10}}}\sqrt{{-{1}}}\usepackage{cmbright}\Huge\$

$\displaystyle={2}\sqrt{{{10}}}{i}={2}{i}\sqrt{{{10}}}\usepackage{cmbright}\Huge\$

The question mark stands for $\displaystyle{2}{i}\usepackage{cmbright}\Huge\$ .