http://www.cut-the-knot.org/pythagoras/Pappus.shtml INSTRUCTIONS: drag the red circles around. Use Flash Turbo Mode. Pappus's Theorem is an important theorem in Projective Geometry, a form of geometry which involves only the straight edge, and not the compass, and only cares about configurations between points and lines, not distances It demonstrates something called Duality; points and lines can be swapped; Every point is on 3 lines, and every line has 3 points; there are 9 lines and 9 points.
