1. The problem statement, all variables and given/known data See attached link 3. The attempt at a solution I am fine up to the point where I have to express in matrix form. My method was, given the equation for the energy, to put this in matrix form and then recover the equations of motion from there (by differentiating and setting the result to zero since total energy constant) . When I divide by ##m/2## in the matrix I recover some terms, but in particular the middle entry I have a missing factor of 1/2 (reason is that the mass of the middle pendulum has a mass of ##2m## - so I don't understand why the solution says otherwise). Also missing factors of 1/2 on entries (1,2) and (3,2). All I have done is put the given expression into matrix form. Is this a viable method? It seems so. ( I would have posted my matrices but when I tried the latex was very ugly and I haven't found a way to get the matrices to be all together rather than one every line) Many thanks.