Remember that $\displaystyle{{x}}^{{\frac{{8}}{{3}}}}={{\left({{x}}^{{8}}\right)}}^{{\frac{{1}}{{3}}}}\usepackage{cmbright}\Huge\$ and $\displaystyle{{y}}^{{-\frac{{4}}{{3}}}}={{\left({{y}}^{{-{{4}}}}\right)}}^{{\frac{{1}}{{3}}}}\usepackage{cmbright}\Huge\$ . Also, $\displaystyle{{y}}^{{-{4}}}=\frac{{1}}{{{y}}^{{4}}}\usepackage{cmbright}\Huge\$ .