Difference between revisions of "2004 USAMO Problems/Problem 6"

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==Problem==
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== Problem ==
 
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(''Zuming Feng'') A circle <math>\omega </math> is inscribed in a quadrilateral <math>ABCD </math>.  Let <math>I </math> be the center of <math>\omega </math>.  Suppose that
A circle <math>\omega </math> is inscribed in a quadrilateral <math>ABCD </math>.  Let <math>I </math> be the center of <math>\omega </math>.  Suppose that
 
 
<center>
 
<center>
 
<math>
 
<math>

Revision as of 13:58, 18 July 2014

Problem

(Zuming Feng) A circle $\omega$ is inscribed in a quadrilateral $ABCD$. Let $I$ be the center of $\omega$. Suppose that

$(AI + DI)^2 + (BI + CI)^2 = (AB + CD)^2$.

Prove that $ABCD$ is an isosceles trapezoid.

Solution

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Resources

2004 USAMO (ProblemsResources)
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