Uploaded April 2025 | Updated September 2026, 2 weeks ago

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This is a short, animated visual proof demonstrating Ptolemy's Theorem, which is an equality about the lengths of the six lines connecting four points randomly selected around a circle. The proof, without words, uses the scaling of three triangles to obtain the result.

Thanks to my son who helped include the awesome sound effects.

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This animation is based on a visual proof by W. Derrick, J. Herstein, Proof Without Words: Ptolemy's Theorem in the November 2012 issue of The College Mathematics Journal: v 43, n 5, November 2012, p 386: jstor.org/stable/10.4169/college.math.j.43.5.386

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