It is easy to demonstrate that amplitude modulation satisfies the superposition principle, whereas angle modulation does not. To be specific, let m₁(t) and m₂(t) be two message signals, and let u₁(t)

and u₂(t) be the corresponding modulated versions. Show that if m₁(t) + m₂(t) frequency modulates a carrier, the modulated signal is not equal to u₁(t) + u₂(t).