This Geobebra applet follows a theorem by Ludolph van Ceulen from 16th century:
A drawing from a book by Ludolph van Ceulen (1540 – 1610) book,
Jonathan Crabtree: Multiplication on the Reals with a Circle
The De Morgan Forum
This Geobebra applet follows a theorem by Ludolph van Ceulen from 16th century:
A drawing from a book by Ludolph van Ceulen (1540 – 1610) book,