Maths Olympiad Prep

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Geometry Difficulty 5.7 AIME, harder Prove it

Let BCB C be a fixed segment in the plane, and let AA be a variable point in the plane not on the line BCB C. Distinct points XX and YY are chosen on the rays CA\overrightarrow{C A} and BA\overrightarrow{B A}, respectively, such that CBX=YCB=BAC\angle C B X=\angle Y C B=\angle B A C. Assume that the tangents to the circumcircle of ABCA B C at BB and CC meet line XYX Y at PP and QQ, respectively, such that the points X,P,YX, P, Y, and QQ are pairwise distinct and lie on the same side of BCB C. Let Ω1\Omega_{1} be the circle through XX and PP centred on BCB C. Similarly, let Ω2\Omega_{2} be the circle through YY and QQ centred on BCB C. Prove that Ω1\Omega_{1} and Ω2\Omega_{2} intersect at two fixed points as AA varies.

Solution

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