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2001 IMO Shortlist Problems/G7

Revision as of 18:50, 20 August 2008 by Minsoens (talk | contribs) (New page: == Problem == Let <math>O</math> be an interior point of acute triangle <math>ABC</math>. Let <math>A_1</math> lie on <math>BC</math> with <math>OA_1</math> perpendicular to <math>BC</math...)
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Problem

Let $O$ be an interior point of acute triangle $ABC$. Let $A_1$ lie on $BC$ with $OA_1$ perpendicular to $BC$. Define $B_1$ on $CA$ and $C_1$ on $AB$ similarly. Prove that $O$ is the circumcenter of $ABC$ if and only if the perimeter of $A_1B_1C_1$ is not less than any one of the perimeters of $AB_1C_1, BC_1A_1$, and $CA_1B_1$.

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