Упростить выражение: (3a-9)/(a^2-4):(a^-9)/(a+2).

\[\frac{3a - 9}{a^{2} - 4}\ :\frac{a^{2} - 9}{a + 2} =\]

\[= \frac{3a - 9}{a^{2} - 4} \cdot \frac{a + 2}{a^{2} - 9} =\]

\[= \frac{3(a + 3)(a + 2)}{(a - 2)(a + 2)(a - 3)(a + 3)} =\]

\[= \frac{3}{(a - 2)(a - 3)}.\]