1. The problem statement, all variables and given/known data The following is a question from an old assignment on coupled oscillators and waves: http://img214.imageshack.us/img214/601/question2.jpg [Broken] 3. The attempt at a solution So, I'm a confused about the meaning of the subscripts fpq and fqp. What do they mean? Do fp and fq refer to partial derivatives of the function? If so what do fpq and fqp mean? I've consulted the textbook physics of vibrations and waves, but I couldn't see what these subscripts stand for. Any help or suggestion would be greatly appreciated.