2sin^2x = cosx + 1
2 * (1 - cos^2x) = cosx + 1
2 - 2cos^2x = cosx + 1
2cox^2x + cosx - 1 = 0
D = 1 + 8 = 9
cosx = (-1 + 3)/4 = 1/2
cosx = (-1-3)/4 = -1
x = +- π/3 + 2πk, k ∈ Z
x = π + 2πn, n ∈ Z
