2sin11π/30-sinπ/30-cos8π/15-cos2π/15 вычислите

Решите задачу:

$2\cdot sin \frac{11\pi }{30}-sin\frac{\pi}{30}-cos\frac{8\pi }{15}-cos\frac{2\pi}{15}=\\\\=2\cdot sin\frac{11\pi}{30}-sin\frac{\pi }{30}-cos(\frac{\pi}{2}+\frac{\pi}{30})-cos(\frac{\pi}{2}-\frac{11\pi}{30})=\\\\=2\cdot sin\frac{11\pi}{30}-sin \frac{\pi }{30} +sin \frac{\pi }{30} -sin\frac{11\pi }{30}=sin\frac{11\pi}{30}=sin66^\circ =cos24^\circ$