9.3 Phasor (4)
Transform a sinusoid to and from the time
domain to the phasor domain:

 (time domain)      (phasor domain)
Amplitude and phase difference are two principal
concerns in the study of voltage and current sinusoids.
Phasor will be defined from the cosine function in all our
proceeding study. If a voltage or current expression is in
the form of a sine, it will be changed to a cosine by
subtracting from the phase.