1. The problem statement, all variables and given/known data Derive from Demoivre's theorem that cos2theta=(costheta)^2-(sintheta)^2 sin2theta=2sin theta costheta 2. Relevant equations 3. The attempt at a solution I really am clueless on this. I considered using (costheta +isintheta)^n, but don't know where to go with this idea.