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2019 Taiwan APMO Preliminary P3

Source: 2019 Taiwan APMO Preliminary

August 23, 2020
triangle inequalityGeometry inequalityalgebra

Problem Statement

Let ABC\triangle ABC be an acute triangle, HH is its orthocenter. AH,BH,CH\overrightarrow{AH},\overrightarrow{BH},\overrightarrow{CH} intersect ABC\triangle ABC's circumcircle at A,B,CA',B',C' respectively. Find the range (minimum value and the maximum upper bound) of AHAA+BHBB+CHCC\dfrac{AH}{AA'}+\dfrac{BH}{BB'}+\dfrac{CH}{CC'}