2017 OIM Problems/Problem 4

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Problem

Let $ABC$ be an acute triangle with $AC > AB$ and $O$ its circumcenter. Let $D$ be a point on the segment $BC$ such that $O$ is inside the triangle $ADC$ and $\angle DAO + \angle ADB = \angle ADC$. We call $P$ and $Q$ the circumcenters of the triangles $ABD$ and $ACD$, respectively, and $M$ the point of intersection of the lines $BP$ and $CQ$. Show that the lines $AM, PQ$ and $BC$ are concurrent.

Note. The circumcenter of a triangle is the center of the circle that passes through the three vertices of the triangle.

~translated into English by Tomas Diaz. ~orders@tomasdiaz.com

Solution

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See also

OIM Problems and Solutions