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CN-TST 2022 Problem 8

  • Test 2

Given a non-right triangle ABCABC with BC>AC>ABBC>AC>AB . Two points P1≠P2P_1 \neq P_2 on the plane satisfy that, for i=1,2i=1,2 , if APi,BPiAP_i, BP_i and CPiCP_i intersect the circumcircle of the triangle ABCABC at Di,EiD_i, E_i , and FiF_i , respectively, then DiEi⊥DiFiD_iE_i \perp D_iF_i and DiEi=DiFi≠0D_iE_i = D_iF_i \neq 0 . Let the line P1P2P_1P_2 intersects the circumcircle of ABCABC at Q1Q_1 and Q2Q_2 . The Simson lines of Q1Q_1 , Q2Q_2 with respect to ABCABC intersect at WW .

Prove that WW lies on the nine-point circle of ABCABC .

Dataset text AI-MO AoPS. Quoted with source.

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