\[\frac{4^{\backslash 2\sqrt{3} - 1}}{2\sqrt{3} + 1} - \frac{4^{\backslash 2\sqrt{3} + 1}}{2\sqrt{3} - 1} =\]
\[= \frac{8\sqrt{3} - 4 - 8\sqrt{3} - 4}{\left( 2\sqrt{3} + 1 \right)\left( 2\sqrt{3} - 1 \right)} =\]
\[= - \frac{8}{4 \cdot 3 - 1} = - \frac{8}{12 - 1} = - \frac{8}{11}.\]