Question

Помогите срочно с алгеброй!

Answer 1

$Cos(\frac{\pi }{6} +\beta)+Cos(\frac{\pi }{6}-\beta)=2Cos\frac{\frac{\pi }{6}+\beta+\frac{\pi }{6}-\beta}{2}Cos\frac{\frac{\pi }{6}+\beta-\frac{\pi }{6}+\beta}{2} =\\\\=2\underbrace{Cos\frac{\pi }{6}}_{\frac{\sqrt{3} }{2}} *\underbrace{Cos\beta}_{0,5}=2*\frac{\sqrt{3} }{2} *\frac{1}{2}=\boxed{\frac{\sqrt{3} }{2}}$