Richard Clark wrote:
and ponder the implication of a negative power, for simplicity:
P1 = 50W @ 90deg
P2 = 50W @ 270deg
what does the math reveal?

Ptotal = P1 + P2 + 2*SQRT(P1*P2)cos(A)

Ptotal = 50 + 50 + 2*SQRT(2500)cos(180)

Ptotal = 50w + 50w - 100w = 0

There's 100 watts of destructive interference.
The two waves are canceled in their original direction
of flow. The energy in the two waves is redistributed
to regions that permit 100 watts of constructive
interference to occur. If the above happens in a
transmission line, the "lost" energy in the canceled
waves will simply be redistributed in the only other
direction available.

micro.magnet.fsu.edu/primer/java/scienceopticsu/interference/waveinteractions/index.html

"... when two waves of equal amplitude and wavelength that are
180-degrees ... out of phase with each other meet, they are not actually
annihilated, ... All of the photon energy present in these waves must
somehow be recovered or redistributed in a new direction, according to
the law of energy conservation ... Instead, upon meeting, the photons
are redistributed to regions that permit constructive interference, so
the effect should be considered as a redistribution of light waves and
photon energy rather than the spontaneous construction or destruction of
light."
--
73, Cecil http://www.w5dxp.com