Be sure that you're dividing the two expressions. Remember that $\displaystyle\frac{{{x}}^{{n}}}{{{x}}^{{m}}}={{x}}^{{{n}-{m}}}\usepackage{cmbright}\Huge\$ and $\displaystyle{{\left({{x}}^{{n}}\right)}}^{{m}}={{x}}^{{{n}{m}}}\usepackage{cmbright}\Huge\$ .