Ptolemy's theorem

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Science and technology

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What Wikipedia says

In Euclidean geometry, Ptolemy's theorem is a relation between the four sides and two diagonals of a cyclic quadrilateral (a quadrilateral whose vertices lie on a common circle). The theorem is named after the Greek astronomer and mathematician Ptolemy (Claudius Ptolemaeus).

Excerpt from the Wikipedia article “Ptolemy's theorem”, under the CC BY-SA 4.0 license. Read the article on Wikipedia

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