2(1-sin^2(x)) +2sin x -2.5 =0

-2sin^2(x) +2sin(x) -0.5=0

sin^2(x) -sin(x) +0.25 =0

sin x = 1/2

x = (-1)^n * arcsin(1/2)+pin

x = (-1)^n *pi/6     +pin