Deacon Dave wrote:
"---am I confused?"

If Dave is confused, I suffer the same confusion. The slope at the
maximum of a sine wave is zero. The slope is maximum at zero crossings
of an undistorted sine wave.

For the power sine wave, though the fact that a minus times a minus is a
plus results in 2x the voltage frequency, dP/dt=0 at maxima.

A question raised in this thread is, how can energy, which is joules per
second times seconds, be zero when the number of seconds is zero? The
answer seems obvious. Zero times anything is zero.

Best regards, Richard Harrison, KB5WZI