Proof of Menelaus using areas

346 Views Asked by At

I've tried to proof Menelaus' theorem using areas, but I've didn't figure out how. Some suggestions would be appreciated.

Menelaus' Theorem states :

enter image description here

Given a triangle ABC and a transversal line that crosses BC, AC and AB at points D, E and F respectively, with D, E and F distinct from A, B and C, then :

$$\frac{AF}{FB} * \frac{BD}{DC} * \frac{CE}{EA} = 1 $$

So far, I've proved Van Aubel's and Ceva's Theorem using areas, but I got stuck at Menelaus.

First, I taught $\frac{[ACB]}{[BCF]} = \frac {AB}{BF}$. And I've applied this for few more triangles, but it didn't work.

(I've noted with $[ABC]$ the area of triangle ABC).

Thanks!