Area of Triangle

Level pending

In triangle ABC, points D, E, and F are on the sides BC, CA and AB such that B D : D C = C E : E A = A F : F B = 1 : 2 BD:DC=CE:EA=AF:FB=1:2 . X is the intersection of AD and BE, Y is the intersection of BE and CF, Z is the intersection of CF and AD. If X Y = 13 , Y Z = 14 , Z X = 15 XY=13, YZ=14, ZX=15 , what is the area of the triangle ABC?


The answer is 588.

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1 solution

Tong Zou
Jan 6, 2014

Let [ A B C ] = k [ABC]=k , let [ A X B ] = x [AXB]=x . Since [ A D B ] = k 3 , [ A B E ] = 2 k 3 [ADB]=\frac{k}{3}, [ABE]=\frac{2k}{3} , we have [ B X D ] = k 3 x , [ A X E ] = 2 k 3 x [BXD]=\frac{k}{3}-x, [AXE]=\frac{2k}{3}-x . Similarly, by the ratio of the bases (with the same height), we have [ C X E ] = k 3 x 2 , [ D X C ] = 2 k 3 2 x [CXE]=\frac{k}{3}-\frac{x}{2}, [DXC]=\frac{2k}{3}-2x . Adding all these up again we have k = [ A B C ] = [ A X B ] + [ B X D ] + [ A X E ] + [ C X E ] + [ D X C ] = 2 k 7 x 2 k=[ABC]=[AXB]+[BXD]+[AXE]+[CXE]+[DXC]=2k-\frac{7x}{2} . So x = 2 k 7 x=\frac{2k}{7} . By the same token, we also have [ A Z C ] = 2 k 7 , [ B Y C ] = 2 k 7 [AZC]=\frac{2k}{7}, [BYC]=\frac{2k}{7} . Therefore [ X Y Z ] = k 7 = 84 [XYZ]=\frac{k}{7}=84 . So k = 588 k=588 .

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