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KöMaL problem A, 2018

Geometry Difficulty 8.0 Shortlist Prove it Hungary

Let PP be a point in the plane of triangle ABCABC. Denote the reflections of AA, BB, CC about PP by A′A', B′B' and C′C', respectively. Let A′′A'', B′′B'', C′′C'' be the reflections of A′A', B′B', C′C' over the lines BCBC, CACA and ABAB, respectively. Let the line A′′B′′A''B'' intersect ACAC at AbA_b and let A′′C′′A''C'' intersect ABAB at a point AcA_c. Denote by ωA\omega_A the circle through the points AA, AbA_b, AcA_c. The circles ωB\omega_B, ωC\omega_C are defined similarly. Prove that ωA\omega_A, ωB\omega_B, ωC\omega_C are coaxial, i.e., they share a common radical axis.

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