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MathNet 2018-part-04 — 181 problems (EN–VI) Question 95

Math Olympiad Vault · MathNet 2018-part-04 — 181 problems (EN–VI)

Question 95

Let $ABCD$ be a cyclic quadrilateral. The line parallel to $BD$ passing through $A$ meets the line parallel to $AC$ passing through $B$ at $E$. The circumcircle of triangle $ABE$ meets the lines $EC$ and $ED$, again, at $F$ and $G$, respectively. Prove that the lines $AB$, $CD$ and $FG$ are either parallel or concurrent.

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