### Sinusoids

The term *sinusoid* means a waveform of the type

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

*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):

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

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