Вычислите sin 2π/5 cos 7π/30-sin 7π/30 cos 2π/5.

\[\sin\frac{2\pi}{5}\cos\frac{7\pi}{30} - \sin\frac{7\pi}{30}\cos\frac{2\pi}{5} =\]

\[= \sin\left( \frac{2\pi}{5} - \frac{7\pi}{5} \right) = \sin{( - \pi)} = 0\]