1. The problem statement, all variables and given/known data Do the Euler-Lagrange equations set to zero for each of the 3 orthogonal coordinates or do you sum them all equal to zero. Do the coordinates have to be orthogonal in order to write separate E-L equations? Or is there no such thing as non-orthogonal coordinates to analyze a problem? My main question is the first one. 2. Relevant equations d/dt(partial L/partial qi dot) - (partial L/partial qi) = 0? 3. The attempt at a solution Not sure. Self-study/No textbook here. Thank you for reading my question. Would the Taylor book on Classical Mechanics explain this well?