Express cos(4θ) and sin(4θ) as polynomials in cos(θ),sin(θ).

Cos 4θ = 2cos^2 2θ  - 1
            = 2 (2 cos^2 θ - 1)^2 - 1
            = 2( 4 cos^4 θ - 4 cos^2 θ  + 1) - 1
            = 8 cos^4 θ  - 8 cos^2 θ  + 1  Answer

sin 4 θ  = 2 sin 2θ cos 2θ
             =  2 ( 2 sinθ cosθ *  (2cos^2θ - 1))
             =  2(4 sin θ cos^3θ - 2 sinθ cosθ)
             = 8 sin θ cos^3θ - 4 sin θ cos θ  

Idon’t understand sorry