## Δευτέρα, 1 Ιανουαρίου 2018

### 2005 JBMO Shortlist 8

Let $O$ be the center of the concentric circles $C_1,C_2$ of radii $3$ and $5$ respectively. Let  $A\in C_1, B\in C_2$  and $C$ point so that triangle $ABC$ is equilateral. Find the maximum length of $[OC]$.

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