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Amplitude modulation

The amplitude of an oscillation cos(ω_b t) can have a variable value. This variable value A cos(ω_a* t) "modulate" the first oscillation: y = A cos(ω_a* t) [ cos(ω_b t) ] An oscillation can be considered as the real part of a complex number that "rotate" in Gauss plane ( cos(ω_a t) + ί sin(ω_a t) ) So the modulated oscillation can be considered as a product between the real parts of two rotating complex numbers. You can animate the point T and change the values of the maximum amplitute and of the angular velocity of the oscillations.