The two sides of each interior angle of a triangle on a sphere determine two congruent lunes with lune angle the same as the interior angle. Show how the three pairs of lunes determined by the three interior angles, a, b, c, cover the sphere with some overlap. (What is the overlap?)Google Image Result for http://upload.wikimedia.org/wikipedia/commons/thumb/5/50/RechtwKugeldreieck.svg/356px-RechtwKugeldreieck.svg.png

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