7. The monotonic increasing interval of the function $f(x)=\log _{\frac{1}{3}}\left(x^{2}-5 x+6\right)$ is $\qquad$ .
二、7. $(-\infty, 2)$.
Because the domain of the function $f(x)=\log _{\frac{1}{3}}\left(x^{2}-5 x+6\right)$ is $x^{2}-5 x+6>0$, which means $x<2$ or $x>3$. Also, $x^{2}-5 x+6=\left(x-\frac{5}{2}\right)^{2}-\frac{1}{4}$, its decreasing interval is $\left(-\infty, \frac{5}{2}\right]$, so the monotonic increasing interval of the function $f(x)=\log \frac{1}{3}\left(x^{2}-5 x+6\right)$ is $(-\infty, 2)$.