1. The problem statement, all variables and given/known data Write down the Lagrangian for a one-dimensional particle moving along the x axis and subject to a force: F=-kx (with k positive). Find the Lagrange equation of motion and solve it. 2. Relevant equations Lagrange: L=T-U (kinetic energy - potential energy) 3. The attempt at a solution All i really need help with is finding the potential energy in this problem. I believe that the kinetic energy is T=(1/2)*m*x', where x' is d/dt(x). I dont understand how to get the potential energy out of that force. Please help, thank you.