1. The problem statement, all variables and given/known data A double pendulum consists of two simple pendula, with one pendulum suspended from the bob of the other. If the two pendula have equal lengths and have bobs of equal mass and if both pendula are confined to move in the same plane, find Lagrange's equations of motion for the system. Do no assume small angles. 2. Relevant equations L=T-U partial L/partial q-(d/dt)(partial L/partial q')+lambda(partial f/partial q) 3. The attempt at a solution Main problem is finding an equation of constraint to use. I know the motion of the pendula must be dependant on each other since they are connected, but not sure how to correctly state that. Also, do I need to set things up piece by piece? Meaning, have an equation of motion for x1,x2,y1,and y2? Or should it be combined?