Trig Equation help?

Question

how do i solve this?
4cos^2x=1

domain must be greater than or equal to -180 and less than or equal to 180.

plz show work.

Answer 1

cos^2 x=1/4

cos x= (1/4)^(1/2) (the square-root of 1/4)

x= cos^-1 ((1/4)^(1/2)) (x equals inverse-cosine of the square-root of 1/4)

x= 1.0471 or pi/3 or 60 degrees

answer could also be -120 degrees or -2.0944 or -2pi/3

Answer 2

cos 2x = 2cos^2 x -1

2(1+cos2x) =1
1+cos2x = 1/2
cos 2x = -1/2
2x = 120
x = 60

check 4 * (1/2)^2 = 1