### Sinusoids

The term sinusoid means a waveform of the type

 (A.1)

Thus, a sinusoid may be defined as a cosine at amplitude , frequency , and phase . (See [84] for a fuller development and discussion.) A sinusoid's phase is in radian units. We may call

the instantaneous phase, as distinguished from the phase offset . Thus, the phase'' of a sinusoid typically refers to its phase offset. The instantaneous frequency of a sinusoid is defined as the derivative of the instantaneous phase with respect to time (see [84] for more):

A discrete-time sinusoid is simply obtained from a continuous-time sinusoid by replacing by in Eq.(A.1):

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