1. The problem statement, all variables and given/known data http://tam.cornell.edu/~als93/wb1413spring2007/assign6.pdf 2. Relevant equations Lagrange equations of motion 3. The attempt at a solution Where do I put the origin? I presume my instructor want something like: x1=L/2*sin(alpha) x2=L/2*sin(beta) y1=L/2*cos(alpha) y2=L/2*cos(alpha) phi1=alpha phi2=beta But where does the angle gamma pops up? And how do I connect the mass on top of the two bars?