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MathNet 2010 — Part 01 Question 139

Math Olympiad Vault · MathNet 2010 — Part 01

Question 139

Points $M$ and $N$ are the midpoints of the sides $AC$ and $BC$ of the triangle $ABC$, respectively.
Prove that a circle passing through $C, M, N$ touches the side $AB$ if and only if $AB = \frac{AC + BC}{\sqrt{2}}$.
(I. Voronovich)