Express cos(4θ)\cos(4\theta)cos(4θ) using the double angle formula repeatedly.
1−8sin2(θ)cos2(θ)1 - 8\sin^2(\theta)\cos^2(\theta)1−8sin2(θ)cos2(θ)
cos4(θ)−sin4(θ)\cos^4(\theta) - \sin^4(\theta)cos4(θ)−sin4(θ)
8cos4(θ)−8cos2(θ)+18\cos^4(\theta) - 8\cos^2(\theta) + 18cos4(θ)−8cos2(θ)+1
4cos(θ)−4sin(θ)4\cos(\theta) - 4\sin(\theta)4cos(θ)−4sin(θ)