# geometry

In a cyclic quadrilateral show that the sum of the products of the opposite sides is equalto the productof the diagnals.

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1. This is known as Ptolemy's Theorem

Here is a page with the proof

http://www.cut-the-knot.org/proofs/ptolemy.shtml

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2. This proof may be useful, but it concerns the ratio of the diagonals, and the ratio of the sum of products of sides connected to the diagonals

The

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3. Looks like Reiny found you the proof you want.

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