lagrangeian problem.... 1. The problem statement, all variables and given/known data in a spring pendulum system the spring is initially in equilibrium at upright position with theta = 0 and elongation (mg)/k, (k is spring constant). total length of spring in equilibrium condition is a with respect to which we define additional deviations in terms of a variable r. write dwn the lagrangian for this system 2. Relevant equations L = kinetic energy - potential energy kinetic energy = 0.5 mv^2 potential = mgh 3. The attempt at a solution i know that the l = kinetic energy - the potential energy...but not exactly sure how to form my equations..please help... i think potential energy would be 0.5(k*x^2) ?