1. The problem statement, all variables and given/known data A masss m ossilates on a spring, find the position as a function of time. 2. Relevant equations F=ma F=-ky 3. The attempt at a solution Well known problem, set m(dx/dt) = -kx get roots of characteristic equation and sub into general solution, x = Aexp(iwt) +Bexp(-iwt) or x = Asin(wt) + Bcos(wt) I'm ok down as far as here however I know this can be written as Ccos(wt-) but I cant see how?