Jim Kelley wrote:
"Power as a scalar quantity does not have direction, and so one could
not for example subtract power "moving" in the other direction by
arbitrarily multiplying by negative one."

Terman did so rather deftly. We make simplifying assumptions and replace
the general case with the special case all the time. Bird defines true
power delivered by the source to the load as the difference between its
forward and reverse power indications. It`s satisfactory in most cases.

Inductive and capacitive reactances are routinely added together to give
the net reactance and it works fine so long as the reactances are pure.
They lie on the same axis but in opposite directions so can be treated
as scalars. Another special case.

Best regards, Richard Harrison, KB5WZI