9.
行列式\( \left|\begin{matrix} \left.\begin{matrix}\cos 20 ^{\circ} \\ \sin 20 ^{\circ}\end{matrix}\right.\end{matrix}\right. \left.\begin{matrix}\left.\begin{matrix}\sin 40 ^{\circ} \\ \cos 40 ^{\circ}\end{matrix}\right.\end{matrix}\right|\)的值是 ______ .