\[\frac{12}{12 - 5\sqrt{6}} - \frac{12}{12 + 5\sqrt{6}} =\]
\[= \frac{12 \cdot \left( 12 + 5\sqrt{6} - 12 + 5\sqrt{6} \right)}{144 - 25 \cdot 6} =\]
\[= \frac{12 \cdot 10\sqrt{6}}{144 - 150} = \frac{120\sqrt{6}}{- 6} =\]
\[= - 20\sqrt{6}\]