On Jan 12, 1:22 pm, Keith Dysart wrote:
P(t) = V(t) * I(t)
As corollary, the power at an instant of time is equal
to the voltage at that instant times the current at
that instant.

You obviously mean the *real* instantaneous voltage times the *real*
instantaneous current. You should say that to avoid confusion.

Seems you need to add 'Re' to that equation to remove the obvious
ambiguity. P(t) = Re[V(t)]*Re[I(t)]

From "Fields and Waves", by Ramo & Whinnery:

W(t) = {Re[Vm*e^j(wt+A1)]}{Re[Im*e^j(wt+A2)]}
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73, Cecil, w5dxp.com