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APMO 2021 - Asian Pacific Mathematics Olympiad Question 3

APMO · APMO 2021 - Asian Pacific Mathematics Olympiad

Question 3

Let $ABCD$ be a cyclic convex quadrilateral with circumcircle $\Gamma$. Let $E=AC\cap BD$, let $L$ be the center of the circle tangent to sides $AB,BC,CD$, and let $M$ be the midpoint of the arc $BC$ of $\Gamma$ not containing $A,D$. Prove that the excenter of triangle $BCE$ opposite $E$ lies on $LM$.

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