Rewrite the radical using a rational exponent. The symbol $\displaystyle\sqrt{{{3}{m}}}\usepackage{cmbright}\Huge\$ means the square root or 2nd root of 3m as in $\displaystyle{\sqrt[{{2}}]{{{3}{m}}}}\usepackage{cmbright}\Huge\$ . The root, 2, determines the denominator of the fraction, so $\displaystyle\frac{{1}}{{2}}\usepackage{cmbright}\Huge\$ will be the rational exponent. Use a grouping symbol to show that the entire expression under the radical will be raised to the one-half power.

$\displaystyle{\sqrt[{}]{{{3}{m}}}}={{\left({3}{m}\right)}}^{{\frac{{1}}{{2}}}}\usepackage{cmbright}\Huge\$