MathDB
3 circles given, equal segments wanted

Source: Balkan BMO Shortlist 2015 G6

August 6, 2019
geometryequal segmentscircumcircleIMO Shortlist

Problem Statement

Let ABAB be a diameter of a circle (ω)(\omega) with centre OO. From an arbitrary point MM on ABAB such that MA<MBMA < MB we draw the circles (ω1)(\omega_1) and (ω2)(\omega_2) with diameters AMAM and BMBM respectively. Let CDCD be an exterior common tangent of (ω1),(ω2)(\omega_1), (\omega_2) such that CC belongs to (ω1)(\omega_1) and DD belongs to (ω2)(\omega_2). The point EE is diametrically opposite to CC with respect to (ω1)(\omega_1) and the tangent to (ω1)(\omega_1) at the point EE intersects (ω2)(\omega_2) at the points F,GF, G. If the line of the common chord of the circumcircles of the triangles CEDCED and CFGCFG intersects the circle (ω)(\omega) at the points K,LK, L and the circle (ω2)(\omega_2) at the point NN (with NN closer to LL), then prove that KC=NLKC = NL.