9. If $\tan \alpha+\tan \beta=25, \cot \alpha+\cot \beta=30$, then $\tan (\alpha+\beta)=$
9. 150 .
$\tan \alpha+\tan \beta=25$, and $\cot \alpha+\cot \beta=\frac{\tan \alpha+\tan \beta}{\tan \alpha \tan \beta}=30$, so $\tan \alpha \cdot \tan \beta=\frac{5}{6}$, hence $\tan (\alpha+\beta)=\frac{25}{1-\frac{5}{6}}=150$.