# A Visual Proof of Girard's Theorem

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Girard's theorem states that the area of a spherical triangle is given by the spherical excess: , where the interior angles of the triangle are , , , and the radius of the sphere is 1.

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Contributed by: Okay Arik (March 2011)

Open content licensed under CC BY-NC-SA

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"A Visual Proof of Girard's Theorem"

http://demonstrations.wolfram.com/AVisualProofOfGirardsTheorem/

Wolfram Demonstrations Project

Published: March 7 2011