Question

найдите значение вырвжения с объяснениями:

$frac{cos(6alpha)cosalpha+sin(6alpha)sinalpha}{sin(pi+5alpha)},</var><var>alpha=frac{pi}{10}$

Answer 1

$frac{cos6alpha*cosalpha+sin6alpha*sinalpha}{sin(pi+5alpha}=frac{cos(6alpha-alpha)}{-sin5alpha}=frac{cos5alpha}{-sin5alpha}=-ctg5alpha=-ctg(5frac{pi}{10})=-ctgfrac{pi}{2}=0$