Question

Найти значения выражений

1) cos (-$frac{61pi}{4}$)

Answer 1

$cos( dfrac{61 pi}{4})=cos( dfrac{5 pi }{4}+2 pi cdot7)=cos( dfrac{5 pi }{4})=- dfrac{ sqrt{2} }{2}$

Answer 2

Cos(- 61π/4) = Cos 61π/4 = Cos(14π + 5π/4) = Cos 5π/4 = Cos(π + π/4) =
= - Cos π/4 = - √2/2