Question

СРОЧНО
упростите выражение b)cosπ/7×cosπ/42-sinπ/7×sinπ/42​

Answer 1

=cos(П/7+П/42)=cos(6п/42+П/42)=cos(7П/42)=cos(П/6)=sqrt(3)/2

Answer 2

Ответ:

$\boxed{\ cos(\alpha +\beta )=cos\alpha \cdot cos\beta -sin\alpha \cdot sin\beta \ }\\\\\\\displaystyle cos\frac{\pi}{7}\cdot cos\frac{\pi}{42}-sin\frac{\pi}{7}\cdot sin\frac{\pi}{42}=cos\Big(\frac{\pi}{7}+\frac{\pi}{42}\Big)=cos\frac{7\pi }{42}=cos\frac{\pi}{6}=\frac{\sqrt3}{2}$