9. In $\triangle A B C$, $\overrightarrow{G A}+\overrightarrow{G B}+\overrightarrow{G C}=0, \overrightarrow{G A} \cdot \overrightarrow{G B}=0$. $\frac{(\tan A+\tan B) \tan C}{\tan A \tan B}=$ $\qquad$ .