1. The problem statement, all variables and given/known data Find an annihilator operator for (cosx)^2 2. Relevant equations 3. The attempt at a solution first derivative -2cosxsinx second derivative 2(sinx)^2 - 2(cosx)^2 third derivative 4sinxcosx +4cosxsinx This isn't getting me anywhere (D^2 + 2) is close but I still have the 2(sinx)^2 term. Any suggestions?