Ptolemy's Theorem (redirected from Ptolemeus theorem)

Ptolemy's theorem [′täl·ə·mēz ‚thir·əm]

(mathematics)

The theorem that a necessary and sufficient condition for a convex quadrilateral to be inscribed in a circle is that the sum of the products of the two pairs of opposite sides equal the product of the diagonals.

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Ptolemy’s Theorem 

the theorem of elementary geometry asserting that the product of the lengths of the diagonals of a quadrangle inscribed in a circle is equal to the sum of the products of the lengths of the opposite sides. The theorem was proved by Ptolemy in the second century.