Question 721544
Let theta = t for simplicity.

-2cos(2t) - 5sin(t) + 3 = 0

-2(1 - 2sin^2(t)) - 5sin(t) + 3 = 0

4sin^2(t) - 5sin(t) + 1 = 0

4sin^2(t) - 4sin(t) - sin(t) + 1 = 0

(4sin(t) - 1)(sin(t) - 1) = 0

t = 0.253, 2.89, pi/2