Ответ:

\[\sin A=\sqrt{1-\left(\frac{12}{13}\right)^2}=\frac5{13}.\]

\[\operatorname{tg}A=\frac{\sin A}{\cos A}=\frac{5/13}{12/13}=\frac5{12}.\]

Ответ: \(\operatorname{tg}A=\frac{5}{12}\).