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Source: China MO 2023 P2

December 29, 2022
geometry

Problem Statement

Let ABC\triangle ABC be an equilateral triangle of side length 1. Let D,E,FD,E,F be points on BC,AC,ABBC,AC,AB respectively, such that DE20=EF22=FD38\frac{DE}{20} = \frac{EF}{22} = \frac{FD}{38}. Let X,Y,ZX,Y,Z be on lines BC,CA,ABBC,CA,AB respectively, such that XYDE,YZEF,ZXFDXY\perp DE, YZ\perp EF, ZX\perp FD. Find all possible values of 1[DEF]+1[XYZ]\frac{1}{[DEF]} + \frac{1}{[XYZ]}.