1. The problem statement, all variables and given/known data Using De Moivre's formula to express sin 4θ in terms of sinθ and cosθ. Using this result, express sin4θcosθ in terms of sinθ only. 2. Relevant equations 3. The attempt at a solution So sin4θ = [cosθ+isinθ]^4 using Binomial .... cos4θ= cos^4(θ) -6cos^2(θ)(sin^2(θ)) +sin^4(θ) & sin4θ= 4cos^3(θ)(sinθ) -4cosθsin^3(θ) so for the last part of the question I assume you replace the cos^2(θ) with 1-sin^2(θ) and then sub this result into cos4θ from above. But I am a little lost about "express sin4θcosθ in terms of sinθ only." where does the sin4θcosθ come from?? Is this the right approach?? I have seen similar question but its just asked to represent sin4θ in terms of cosθ or visa-verca the extra cos term is messing with my head ??? Thanks.