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2013 JBMO Shortlist G2

Source: 2013 JBMO Shortlist G2

October 8, 2017
geometryJBMO

Problem Statement

Circles ω1{\omega_1} , ω2{\omega_2} are externally tangent at point M and tangent internally with circle ω3{\omega_3} at points K{K} and LL respectively. Let A{A} and B{B} be the points that their common tangent at point M{M} of circles ω1{\omega_1} and ω2{\omega_2} intersect with circle ω3.{\omega_3.} Prove that if KAB=LAB{\angle KAB=\angle LAB} then the segment AB{AB} is diameter of circle ω3.{\omega_3.}
Theoklitos Paragyiou (Cyprus)