- John Golden
An illustration of Blaise Pascal's early theorem in projective geometry. He conjectured this when he was 16, though his proof is lost to history. His lemmas for this theorem seem to indicate that he did have a successful proof as they match with modern approaches to the result. One consequence of this theorem is that five points (no 3 of which are collinear) determine a conic. See a nice explanation at Cut-the-Knot: http://www.cut-the-knot.org/Curriculum/Geometry/PascalConics.shtml
More GeoGebra at mathhombre.blogspot.com.