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A, B', P, Q concyclic wanted, 2 altitudes and 2 circles related

Source: 2022 Saudi Arabia JBMO TST 1.2

November 1, 2022
geometryconcurrency

Problem Statement

Let BB′BB', CC′CC' be the altitudes of an acute-angled triangle ABCABC. Two circles passing through AA and C′C' are tangent to BCBC at points PP and QQ. Prove that A,B′,P,QA, B', P, Q are concyclic.
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