Pythagoras Interactive

Eureka! An interactive illustration of the Pythagorean Theorem. Drag the legs of the right triangle and watch the three squares transform in real time. Every side shows its length, every square its area — in radical form when needed, so you'll see 2√2 rather than 2.828. Slide through a visual demonstration of Euclid's original proof from Book I of the Elements. Understand why the theorem is always true, not just what it claims.