Answer:
α = 60, 120, 240, 300 (0 =< α <= 360).
If you require a general solution in radians the answer is
α = π(n - 2/3) where n is an integer and
α = π(n - 4/3) where n is an integer.
Step-by-step explanation:
4 cos^2 α = 1
cos^2 α = 1/4
cos α = +/- 1/2
For angles 0 =< α <= 360
α = 60, 300, 120, 240.
