Упростите выражение: (a-18)/(2a-12)-(a-6)/(2a+12)+50/(a^2-36).

\[\frac{a - 18}{2a - 12} - \frac{a - 6}{2a + 12} + \frac{50}{a^{2} - 36} =\]

\[= \frac{- 44}{2\left( a^{2} - 36 \right)} = - \frac{22}{a^{2} - 36} =\]

\[= \frac{22}{36 - a^{2}}.\]