B) sin + sin; 6 7

B) Используем формулу суммы синусов:$$sin(x) + sin(y) = 2sin(\frac{x+y}{2})cos(\frac{x-y}{2})$$

В нашем случае $$x = \frac{\pi}{6}$$ и $$y = \frac{\pi}{7}$$.

$$sin(\frac{\pi}{6}) + sin(\frac{\pi}{7}) = 2sin(\frac{\frac{\pi}{6} + \frac{\pi}{7}}{2})cos(\frac{\frac{\pi}{6} - \frac{\pi}{7}}{2}) = 2sin(\frac{\frac{13\pi}{42}}{2})cos(\frac{\frac{\pi}{42}}{2}) = 2sin(\frac{13\pi}{84})cos(\frac{\pi}{84})$$.

Ответ: $$2sin(\frac{13\pi}{84})cos(\frac{\pi}{84})$$.