#andy
\[\begin{array}{l}
\tan \alpha = \frac{{AC}}{{AB}}\\
\frac{5}{{12}} = \frac{{AC}}{6}\\
\Rightarrow AC = \frac{{6 \times 5}}{{12}} \Rightarrow 2,5(cm)\\
ABC \bot A\\
\Rightarrow A{C^2} = A{C^2}\\
\Rightarrow {6^2} + 2,{5^2}\\
\Rightarrow BC = 6,5cm
\end{array}\]