Definition of Periodic CT Signal
x(t) is periodic if there existes T>0 such that x(t)=x(T+t)
Example
Let's look at: $ x(t)=3*cos(3t) $, we know that the fudamental period of x(t) is
$ w_0=2*\pi/T $
$ x(t)=3*cos(3t) $
$ =\frac{3}{2}[(e^{j*3*t})+(e^{-j*3*t})] $
$ =\frac{3}{2}(e^{j*3*t})+\frac{3}{2}(e^{-j*3*t}) $
so we can see that when k=1
