## Quick Reference

The following theorem, due to Menelaus of Alexandria:

Theorem

Let *L*, *M* and *N* be points on the sides *BC*, *CA* and *AB* of a triangle (possibly extended). Then *L*, *M* and *N* are collinear if and only if

(Note that *BC*, for example, is considered to be directed from *B* to *C* so that *LC*, for example, is positive if *LC* is in the same direction as *BC* and negative if it is in the opposite direction; see measure.) See Ceva's Theorem.

*Subjects:*
Mathematics.

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