$$
\begin{array}{l}
\text { If } \mathrm{A}, \mathrm{B}, \mathrm{C} \text { are the angles of a triangle, }\\
\text { prove that }\left|\begin{array}{ccc}
-\cos C & \sin C & \cos C \\
\sin 2 A & 0 & \sin 2 B \\
\sin (A-B) & \cos (A-B) & \sin (A-B)
\end{array}\right|=\sin 2 C
\end{array}
$$