Sin(3pi/14)-sin(pi/14)-sin(5pi/14)Решите, или хотя бы подскажите ход действий. P.S:...

$sin\frac{3\pi}{14}-sin\frac{\pi}{14}-sin\frac{5\pi}{14} = \\\\$

Домножим и поделим на $cos\frac{\pi}{14}$

$\frac{(sin\frac{3\pi}{14}-sin\frac{\pi}{14}-sin\frac{5\pi}{14})cos\frac{\pi}{14}}{cos\frac{\pi}{14}} = \\\\ sin\frac{3\pi}{14}*cos\frac{\pi}{14} = 0.5sin\frac{\pi}{7}+0.5cos\frac{3\pi}{14}\\\\ -sin\frac{\pi}{14}*cos\frac{\pi}{14} = -0.5sin\frac{\pi}{7}\\\\ -sin\frac{5\pi}{14}*cos\frac{\pi}{14} = -0.5cos\frac{\pi}{14}-0.5cos\frac{3\pi}{14}$

суммируя

$\frac{-0.5cos\frac{\pi}{14}}{cos\frac{\pi}{14}} = -\frac{1}{2}$