[tex]\displaystyle\\
\text{Aplicam teorema sinusurilor.}\\\\
\frac{AB}{\sin C} = \frac{BC}{\sin A} \\\\\\
\frac{12}{\sin 60^o} = \frac{8}{\sin A} \\\\\\
\sin A = \frac{8\sin 60^0}{12}= \frac{2\sin 60^0}{3}=\frac{2}{3}\cdot\sin 60^0=\frac{2}{3}\cdot \frac{ \sqrt{3} }{2} =\boxed{\frac{ \sqrt{3} }{3}}[/tex]