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MathNet 2008-part-01 — 165 problems (EN–VI) Question 92

Math Olympiad Vault · MathNet 2008-part-01 — 165 problems (EN–VI)

Question 92

Let $M$ be the midpoint of the segment $AB$ and $C$ be an interior point of the segment $AB$, $C \neq M$. The isosceles triangles $ACK$ ($AK = CK$) and $BCL$ ($BL = CL$) lie in the same halfplane with respect to $AB$ and are such that the points $K, C, L$ and $M$ are concyclic. Prove that either $KL \parallel AB$ or $KA \perp LB$.