Алгебра: Вопрос в картинках...

Решите задачу:

$sin(x + \frac{2\pi}{3} ) sin(x - \frac{\pi}{3}) = \\\ =0,5(cos(x + \frac{2\pi}{3}-x+ \frac{\pi}{3})-cos(x + \frac{2\pi}{3}+x - \frac{\pi}{3}))= \\\ =0,5(cos\pi-cos(2x + \frac{\pi}{3} ))=-0.5-0.5cos(2x + \frac{\pi}{3} )$

$sin(x + \frac{\pi}{4} ) sin(x - \frac{\pi}{3}) = \\\ =0,5(cos(x + \frac{\pi}{4}-x+ \frac{\pi}{3})-cos(x + \frac{\pi}{4}+x - \frac{\pi}{3}))= \\\ =0,5(cos \frac{7\pi}{12}-cos(2x- \frac{\pi}{12}))= 0,5cos \frac{7\pi}{12}-0.5cos(2x- \frac{\pi}{12})$