Using formulas cos θ =1/2(e^iθ + e^−iθ) and sin θ =1/2i(e^iθ − e^−iθ)

Question

to obtain the identity sin 4 θ =1/8 (cos 4θ − 4 cos 2θ + 3)?

Answer 1

Right hand side identiy

= Left hand side identity.