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Angle Bisector in a Parallelogram

Source: SMO Senior 2019 Q1

June 29, 2019
geometryangle bisectorparallelogramcircumcircle

Problem Statement

In a parallelogram ABCDABCD, the bisector of ∠A\angle A intersects BCBC at MM and the extension of DCDC at NN. Let OO be the circumcircle of the triangle MCNMCN. Prove that ∠OBC=∠ODC\angle OBC = \angle ODC
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