In the triangle $ABC$ , the angle bisector $AD$ divides the side $BC$ into the ratio $BD: DC = 2: 1$. In what ratio, does the median $CE$ divide this bisector?
Problem
Source: Vyacheslav Yasinsky Geometry Olympiad 2017 X-XI p6 [Ukranie]
Tags: geometry, angle bisector, ratio, median
22.09.2018 08:49
MISTAKE
22.09.2018 09:32
Let $CE$ meet $AD$ at $F$.Now,$\frac{AF}{DF}=\frac{AC}{CD}\times\frac{\sin \angle ACF}{\sin \angle FCD}$.We have $\frac{AE}{BE}=\frac{AC}{BC}\times\frac{\sin \angle ACF}{\sin \angle FCD}$ or $\frac{\sin \angle ACF}{\sin \angle FCD}=\frac{BC}{AC}$.Therefore,$\frac{AF}{DF}=\frac{BC}{CD}=\frac{3}{1}$.
31.10.2018 20:58
Let $ AD \cap CE $, Using Barycentric Coordinates, It's easy to find, $$P\equiv (x:1:2) \text { and } P\equiv (1:1:z) \implies \boxed {P\equiv (1:1:2) \equiv (\frac {1}{4} , \frac {1}{4}, \frac {1}{2})} $$ WLOG, Let's assume $[ABC]=1$, We easily get, $$[APC]=\frac {1}{4} ,[ABD]=\frac {2}{3}, [APB]=\frac {1}{2}, [BPD]=\frac {1}{6},[BPC]=[BPD]+[PDC]=\frac {1}{6}+[PDC]=\frac {1}{4} \implies [PDC]=\frac {1}{12} $$ Hence, $$\frac{[APC]}{[PDC]}=\frac {AP}{DP}=\frac {\tfrac {1}{4}}{\tfrac {1}{12}}=3$$ Therefore, $$\boxed {AP:DP=3:1} $$