1. The problem statement, all variables and given/known data Show that d(v^2)/dt = 2 . (d^2r/dt^2) . (dr/dt) HINT: v^2 = ||dr/dt||^2 = dr/dt . dr/dt 2. Relevant equations 3. The attempt at a solution I did it another method: d(v^2)/dt = d/dv(v^2) . dv/dt --------------chain rule = 2v . dv/dt since v=dr/dt and dv/dt = d^2r/dt^2 therefore = 2 . (d^2r/dt^2) . (dr/dt) Is there a more rigorous method to solving this, using the 'HINT' it gave me. I can't quite figure it out.