Question

Помогите, пожалуйста!!!
Вычислите:
cos (-5π/3)+ cos (π/3)+ cos π+cos (-π/4)

Answer 1

$\displaystyle \cos\bigg(-\frac{5\pi}3\bigg)+\cos\bigg(\frac{\pi}{3}\bigg)+\cos\pi+\cos\bigg(-\frac{\pi}4\bigg)=\frac{1}2+\frac{1}2-1+\frac{\sqrt{2}}{2}=\boxed{\frac{\sqrt2}2}$