MathDB
line JK of intersection points of 2 lines passes through the midpoint of BC

Source: Rioplatense Olympiad 2018 level 3 p4

December 11, 2018
geometrymidpointintersectionscircumcirclearc midpoint

Problem Statement

Let ABCABC be an acute triangle with AC>ABAC> AB. be Γ\Gamma the circumcircle circumscribed to the triangle ABCABC and DD the midpoint of the smallest arc BCBC of this circle. Let EE and FF points of the segments ABAB and ACAC respectively such that AE=AFAE = AF. Let PAP \neq A be the second intersection point of the circumcircle circumscribed to AEFAEF with Γ\Gamma. Let GG and HH be the intersections of lines PEPE and PFPF with Γ\Gamma other than PP, respectively. Let JJ and KK be the intersection points of lines DGDG and DHDH with lines ABAB and ACAC respectively. Show that the JKJK line passes through the midpoint of BCBC