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Easy geometry

Source: CJMO 2022 P1

March 12, 2022
geometryaltitudes

Problem Statement

Let △ABC\triangle{ABC} has circumcircle Γ\Gamma, drop the perpendicular line from AA to BCBC and meet Γ\Gamma at point DD, similarly, altitude from BB to ACAC meets Γ\Gamma at EE. Prove that if AB=DE,∠ACB=60∘AB=DE, \angle{ACB}=60^{\circ} (sorry it is from my memory I can't remember the exact problem, but it means the same)
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