Menelaus's Theorem
The way two cevians of a triangle divide each other and two of the triangle's sides.
\(\large{ \frac{A\;D}{D\;B} \; \frac{B\;P}{P\;F} \; \frac{F\;C}{C\;A} = 1 }\)
If three points are collinear (D, P, C), then \(\large{ \frac{A\;D}{D\;B} \; \frac{B\;P}{P\;F} \; \frac{F\;C}{C\;A} = 1 }\)