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MathNet 2025-part-01 — 187 problems (EN–VI) Question 27

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

Question 27

Given a circle $\omega$ and two points $A, B$ outside $\omega$. A quadrilateral inscribed in $\omega$ is called "good" if one pair of opposite sides intersects at $A$ and the other pair intersects at $B$.
Assume that at least one good quadrilateral exists. Prove that there exists a good quadrilateral $\Gamma$ such that every other good quadrilateral has area smaller than $\Gamma$.