Question

How do you solve this? Use a double-angle identity to find the exact value of each expression.

cos4 pi/3

Answer 1

`cos({4 pi}/3) = cos ( 2 ({2pi}/3)) = 2 cos^2 ({2pi}/3) -1 = 2 cos ^2 120^circ -1 = 2(-1/2)^2 -1 = -1/2`