Menelaus' theorem

Menelaus' theorem is used when you have a transversal (XYZ) in a triangle.

The diagrams below explain this far better than text can. The first illustrates what the theorem actually means, the second describes its proof.

The converse of Menalaus' theorem is also true; ie if the ratios multiply to give -1 then X, Y and Z are collinear.

To download this Geogebra file click here.

To download this Geogebra file click here.