Let points A, B, and C be equally spaced around a circle, and let point P lie on the arc between A and B.
Prove that PA + PB = PC.
Ptolemy's theorem gives
PC*AB = PA*BC + PB*CA
Points A, B, and C equally spaced
around the circle gives
AB = BC = CA
Therefore,
PC = PA + PB
QED

Posted by Bractals
on 20170317 15:17:05 