Any radical in the form $\displaystyle{\sqrt[{{n}}]{{{{c}}^{{x}}}}}\usepackage{cmbright}\Huge\$ can be rewritten as $\displaystyle{{c}}^{{\frac{{x}}{{n}}}}\usepackage{cmbright}\Huge\$ .

So: $\displaystyle{\sqrt[{{5}}]{{{{c}}^{{8}}}}}={{c}}^{{\frac{{8}}{{5}}}}\usepackage{cmbright}\Huge\$