theta = x
0<x<2pi
(cos x) (sin 2x)-2 sin x + 2 = 0
(cos x) (sin 2x) - 2 sin x = -2
(cos x ) (2 (sin x) (cos x) ) - 2 sin x = -2
(2 sin x )( cos^2 (x) - 1) = -2
(2 sin x) (-sin^2(x)) = -2
-2 sin^3 (x) = -2
sin^3 (x) = 1
x = pi/2
Answer was confirmed with Mathematica.