Solve that equation : `costheta+cos3theta-2cos2theta=0`

Solve that equation: cos theta+cos3 theta-2cos2 theta=0

Solve the equation: sin2theta+cos3theta=0

Solve: cos3theta+2costheta=0

Solve: cos3theta+costheta=0

costheta.cos2theta.cos3theta=1/4

cos2 theta+3cos theta=0

Solve the following equation: cos theta+cos3 theta-cos2 theta=0

Solve the equation 3-2cos theta-4sin theta-cos2 theta+sin2 theta=0

Solve cos theta+cos 3 theta-2 cos 2 theta=0 .

Solve the following trigonometric equations, (ii) cos 3theta+costheta-2cos theta=0 (iii) cos 3theta+8cos^(3)theta=0