For the real signal $f(t),$ show that if it is band-limited to the range
$$\nu_0 - \frac{1}{2} \alpha \leq \nu \leq \nu_0 + \frac{1}{2} > \alpha$$ (where $\nu_0 >\frac{1}{2} \alpha >0$), then the modulus squared of the analytic signal $|f_a (t)|^2$ is band-limited to the frequency range $-\alpha \leq \nu \leq \alpha.$
How should I approach this problem? I am very confused because no explicit expression for $f(t)$ is given, so I don't know how to find $|f(t)|^2$ (the envelope of $f(t)$ squared).
Any help would be greatly appreciated.