1. The problem statement, all variables and given/known data I was given a problem with a list of sums of sinusoidal signals, such as Example that I made up: x(t)=cos(t)+5sin(5*t). The problem asks if a given expression could be a Fourier expansion. 2. Relevant equations 3. The attempt at a solution My guess is that it has something to do with 5 being an integer multiple of 1.