Suppose we have the signal $$x(t) = e^{j\omega_1 t} + e^{j\omega_2 t} + e^{j\omega_3 t},$$ where all the frequencies are rationally related (that is, the ratio of any pair of frequencies is a rational number).
How do I prove the fact that the fundamental frequency of the expression above is given by $\omega_0 = \gcd(\omega_1, \omega_2, \omega_3)$?
My attempt is as follows: assume that the signal has a fundamental period $T_0$ which is related to the fundamental frequency by $\omega_0 = 2\pi/T_0$. Now for the signal to be periodic with this period as the fundamental period the following equations must be satisfied $$\omega_1 T_0 = 2 \pi l$$ $$\omega_2 T_0 = 2\pi m$$ $$\omega_3 T_0 = 2\pi n,$$ where $l, m, n \in \mathbb{Z}$ and their values are such that $T_0$ is minimized.
- Where do I go from here?
- How do I show that the fundamental frequency $\omega_0 = 2\pi/T_0$ is the greatest common divisor of $\omega_1$, $\omega_2$, and $\omega_3$?