Monday, April 12, 2021

Ptolemy again

 My last post was about Ptolemy's theorem.  In the meantime, I've come across a cool "proof without words" for this.


I can see how, knowing that we want ac + bd could lead you to work on scaling triangles into the parallelogram, which would then give all the angles for the central triangle (although note the switch in order for gamma and delta).

It's simply beautiful.