Question

Cos^2 phi/6 - sin^2 3phi/4 + 8 sin phi/4 cos 3phi/4 = ...

Answer 1

Π/6 = 180 /6= 30°
3π/4 = 3(180)/4 = 135°
π/4 = 180/4 = 45°

cos² 30 - sin² 135 + 8 sin 45. cos 135=
= (¹/₂ √3)² - (-¹/₂ √2) + 8 (¹/₂√2)(-¹/₂√2)
= 3/4 - 1/2 - 4
= - 15/4