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MathNet 2025-part-01 — 187 problems (EN–VI) Question 169

Math Olympiad Vault · MathNet 2025-part-01 — 187 problems (EN–VI)

Question 169

Let $ABCD$ be a parallelogram and let $M$ be the intersection point of the diagonals. The circumcircle of $\triangle ABM$ intersects the line segment $AD$ at $E \neq A$, and the circumcircle of $\triangle EMD$ intersects the line segment $BE$ at the point $F \neq E$.
Prove that $\angle ACB = \angle DCF$.

Question illustration