Pappus's hexagon theorem

Pappus's hexagon theorem is a result in projective geometry named after the ancient Greek mathematician Pappus of Alexandria. The theorem states that if you have a hexagon inscribed in two lines (i.e., pairs of opposite vertices of the hexagon lie on each of the two lines), the three pairs of opposite sides of the hexagon, when extended, will meet at three points that are collinear (lie on a straight line).