In the context of basic mathematical representations, an amplitude is a measure of the magnitude or intensity of a quantity, such as a waveform or oscillation. The amplitude can be positive or negative, representing the magnitude in either direction from a reference point.
For example, in a simple sine wave, the amplitude is the distance from the peak of the waveform to the equilibrium or zero reference level. If the waveform extends above the zero reference level, the amplitude is positive. Conversely, if the waveform extends below the zero reference level, the amplitude is negative.
In the case of amplitude modulation (AM) used in communications, the amplitude of the carrier wave is modulated by the information-bearing signal. This modulation can result in positive or negative variations in the amplitude of the carrier wave, representing the encoded information.
So, to answer your question, yes, amplitudes can be negative depending on the reference point and the direction of the waveform or signal being measured.