Menelaus' Theorem

- Mathematics & Logic -
Pure Mathematics Dictionary
A criterion for collinearity of three points where a transversal meets the sides (or their extensions) of a triangle: for points D on BC, E on CA, F on AB lying on a line, the directed product (BD/DC)·(CE/EA)·(AF/FB) = −1. It determines when a line intersects the three (possibly extended) sides of a triangle in specified points.