The Compendium Geometry is an eBook providing facts, formulas and explanations about geometry.

Thales' Theorem

The theorem of Thales can be formulated in two ways:
  • The inscribed angle in a semicircle is always a right angle.
  • In a right triangle, the right angle is always located on the (semi)circle whose center is at the middle of side c having a radius of c/2. This circle is always the circumcircle of the right triangle.
The semicircle over the hypothenuse of a right triangle is sometimes also called "Thales circle".

Last Update: 2010-12-06