2\sin2θ=1+\cosθimplies2(1−\cos2θ)=1+\cosθ
2−2\cos2θ=1+\cosθ
2−2\cos2θ−1−\cosθ=0
2\cos2θ+\cosθ−1=0
2\cos2θ+2\cosθ−\cosθ−1=0implies2\cosθ(\cosθ+1)−1(\cosθ+1)=0
(2\cosθ−1)(\cosθ+1)=0implies\cosθ=12
θ=\cos−112=60°