Archimedes' Twin Circles
Archimedes' Twin Circles
Pick any three points on a line and use each pair of them
to define a semicircle, as shown.
Now draw a perpendicular between the two smaller semicircles.
The two red circles will always have the same area.
credit: Greg Ross
http://www.futilitycloset.com/2014/03/20/archimedes-twin-circles/
Image: Wikimedia Commons
also see: John Golden's work at
http://mathhombre.blogspot.com/2014/03/archimedes-twin-circles.html