An interactive applet and associated web page that illustrate Pythagoras' Theorem. The applet shows a right triangle that can be resized by dragging any vertex. As it is being dragged the formula is continuously recalculated to show that the the theorem always holds for any right triangle. The formula can be turned off to facilitate classroom discussions.

Applet can be enlarged to full screen size for use with a classroom projector. After use in the classroom, student can access it again from any web browser at home or in the library with no login required.

This resource is a component of the Math Open Reference Interactive Geometry textbook project at http://www.mathopenref.com.