(See attached file for full problem description)
A signal x(t) of finite energy is applied to a square-law device whose output y(t) is given by
y(t) = x2(t)
The spectrum of x(t) is limited to the frequency interval -W ≤ f ≤ W. Show that the spectrum of y(t) is limited to -2W ≤ f ≤ 2W.
(Hint: Express y(t) as x(t) multiplied by itself.)