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Show that in any circumscribed polygon, there exist three sides which could form a triangle.
Been on it for a while starting with quadrilaterals and trying to connect some properties and proved for quadrilaterals. How to prove the general case.
Your claim follows immediately from taking the longest side and the two sides next to it, by using the basic property that the two tangent line segments from a point to a circle are of the same length.
[My original answer below was due to my misunderstanding of "circumscribed".]
I have proven that your proof for quadrilaterals is wrong, and hence your property is too beautiful to be true. Let $ABCD$ be a trapezium such that $AD \parallel CD$ and $(\overline{AB},\overline{CD},\overline{BC},\overline{AD}) = (9,6,2,2)$. Clearly $ABCD$ exists and is cyclic, but no three of its sides can be arranged to form a triangle.
Your claim follows immediately from taking the longest side and the two sides next to it, by using the basic property that the two tangent line segments from a point to a circle are of the same length.
[My original answer below was due to my misunderstanding of "circumscribed".]
I have proven that your proof for quadrilaterals is wrong, and hence your property is too beautiful to be true. Let $ABCD$ be a trapezium such that $AD \parallel CD$ and $(\overline{AB},\overline{CD},\overline{BC},\overline{AD}) = (9,6,2,2)$. Clearly $ABCD$ exists and is cyclic, but no three of its sides can be arranged to form a triangle.