Menelaus theorem

A theorem on the relations between the lengths of the segments on the sides of a triangle determined by an intersecting straight line. It asserts that if the given line intersects the sides of a triangle (or their extensions) at the points , and , then

Menelaus' theorem is a particular case of the Carnot theorem; it can be generalized to the case of a polygon. Thus, suppose that a straight line intersects the edges of a polygon at the respective points . Then the following relation is valid:

The theorem was proved by Menelaus (1st century) and apparently it was known to Euclid (3rd century B.C.).

Figure: m063400a

References

[a1]	B.L. van der Waerden, "Science awakening" , 1 , Noordhoff & Oxford Univ. Press (1961) pp. 275 (Translated from Dutch)