((r^n)^2)/(r^(6-2n))
$$\\\frac{(r^n)^2}{r^{6-2n}}\\\\ =\frac{(r^{2n})}{r^{6-2n}}\\\\ =r^{2n-(6-2n)}\\\\ =r^{2n-6+2n)}\\\\ =r^{4n-6}\\\\$$
$${\frac{{{\mathtt{r}}}^{{\mathtt{4}}{n}}}{{{\mathtt{r}}}^{{\mathtt{6}}}}}$$
= $${{\mathtt{r}}}^{\left({\mathtt{4}}{n}{\mathtt{\,-\,}}{\mathtt{6}}\right)}$$
sorry Badinage - your answer was not up yet when I started.