In triangle ABC, points D, E, and F are on the sides BC, CA and AB such that . 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 , what is the area of the triangle ABC?
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Let [ A B C ] = k , let [ A X B ] = x . Since [ A D B ] = 3 k , [ A B E ] = 3 2 k , we have [ B X D ] = 3 k − x , [ A X E ] = 3 2 k − x . Similarly, by the ratio of the bases (with the same height), we have [ C X E ] = 3 k − 2 x , [ D X C ] = 3 2 k − 2 x . 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 − 2 7 x . So x = 7 2 k . By the same token, we also have [ A Z C ] = 7 2 k , [ B Y C ] = 7 2 k . Therefore [ X Y Z ] = 7 k = 8 4 . So k = 5 8 8 .