MathDB
JK bisects BC, incenter, arc midpoint of circumcircle, AE = AF

Source: 2018 Cono Sur Shortlist G4

August 25, 2021
geometryincentercircumcircle

Problem Statement

Let ABCABC be an acute triangle with AC>ABAC > AB. Let Γ\Gamma be the circle circumscribed to the triangle ABCABC and DD the midpoint of the smaller arc BCBC of this circle. Let II be the incenter of ABCABC and let EE and FF be points on sides ABAB and ACAC, respectively, such that AE=AFAE = AF and II lies on the segment EFEF. Let PP be the second intersection point of the circumcircle of the triangle AEFAEF with Γ\Gamma with PAP \ne A. Let GG and HH be the intersection points of the lines PEPE and PFPF with Γ\Gamma different from PP, respectively. Let JJ and KK be the intersection points of lines DGDG and DHDH with lines AB and ACAC, respectively. Show that the line JKJK passes through the midpoint of BCBC.