1. The problem statement, all variables and given/known data Is the function cosx + cos(sqrt(2)x) is periodic? 2. Relevant equations cos(x)=cos(x+2pi) 3. The attempt at a solution For the above function to be periodic: cosx + cos(sqrt(2)x) = cos(x+T) + cos(sqrt(2)(x + T)) Does that imply that 2pi = T AND 2pi = sqrt(2)T, ergo there is no such T?