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# biangle

In spherical geometry, it is possible to form a polygon with only two sides. Thus, we have the following definition:

A *biangle* is a two-sided polygon that is strictly contained in one hemisphere of the sphere that is serving as the model for spherical geometry.

Given a biangle, its vertices must be antipodal points, and its two angles must be congruent. Therefore, every biangle is equiangular. Since each side of a biangle is half of a great circle, every biangle is equilateral. Hence, every biangle is regular.

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## Mathematics Subject Classification

51M10*no label found*51-00

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