sin (pi -x) = cos (pi +2x)
sin x = -cos 2x
sin x +1-2sin ^2 (x) = 0
2a^2 +a +1 = 0
a = 1/2 a = -1
sin x = 1/2
x = (-1)^n * (pi/6) +pin
sin x = -1
x = -pi/2 +2pin
