#### Why Phasors are Important

Linear, time-invariant (LTI) systems can be said to perform only four operations on a signal: copying, scaling, delaying, and adding. As a result, each output is always a*linear combination*of delayed copies of the input signal(s). (A

*linear combination*is simply a weighted sum, as discussed in §5.6.) In any linear combination of delayed copies of a complex sinusoid

*i.e.*, by expressing it as an inverse Fourier transform).

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