2cosx+cos^2 x=2-sin^2 x

2cosx+cos^2x=2-(1-cos^2x) 2cosx+cos^2x-2+1-cos^2x=0 2cosx=1 cosx=1/2 x₁=pi/3+2pi*n, n∈Z x₂=-pi/3+2pi*n, n∈Z