MathDB
Brocard's theorem FTW

Source: Latvia TST for Baltic Way 2020 P11

October 18, 2020
geometryFTW

Problem Statement

Circle centred at point OO intersects sides AC,ABAC, AB of triangle △ABC\triangle ABC at points B1B_1 and C1C_1 respectively and passes through points B,CB,C. It is known that lines AO,CC1,BB1AO, CC_1, BB_1 are concurrent. Prove that △ABC\triangle ABC is isosceles.
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