Given equations is cos 3x + cos x – cox 2x = 0

⇒

⇒ 2 cos2x cos x – cos 2x = 0

⇒ cos 2x( 2cos x – 1) = 0

⇒ cos 2x= 0 or 2 cos x – 1 = 0

⇒ cos 2x= 0 or cos x = 1/2

∴where n ϵ Z and Z is set of integers

⇒ where n ∈Z and z is set of integers