### Plotting Complex Sinusoids versus Frequency

As discussed in the previous section, we regard the signal

*positive-frequency sinusoid*when . In a manner analogous to spectral magnitude plots (discussed in §4.1.6), we can plot this complex sinusoid over a frequency axis as a vertical line of length at the point , as shown in Fig.4.10. Such a plot of amplitude versus frequency may be called a

*spectral plot*, or

*spectral representation*[44] of the (zero-phase) complex sinusoid.

figure[htbp]
More generally, however, a complex sinusoid has both an amplitude and
a *phase* (or, equivalently, a *complex amplitude*):

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Positive and Negative Frequencies