Помогите с матешей СРОЧНОО

cos2x = cos^2x - sin^2x
2cos^2x - 2sin^2x - 3cosx + 2 = 0 <=> 2cos^2x - 2(1- cos^2x) - 3cosx + 2 = 0 <=>
4cos^2x -2 + 2 - 3cosx = 0 <=> cos(x) = 0 or cos(x) = 3/4
x = pi/2 + pi*k for integer k
x = +-arccos(3/4) + 2pi*k for integer k

integer = целое