non-Euclidean geometry: Hyperbolic Geometry

In hyperbolic geometry the two rays extending out in either direction from a point P and not meeting a line L are considered distinct parallels to L; among the results of this geometry is the theorem that the sum of the angles of a triangle is less than 180°. One surprising result is that there is a finite upper limit on the area of a triangle, this maximum corresponding to a triangle all of whose sides are parallel and all of whose angles are zero. Lobachevsky's geometry is called hyperbolic because a line in the hyperbolic plane has two points at infinity, just as a hyperbola has two asymptotes. The analogy used in considering this geometry involves the lines and figures drawn on a saddleshaped surface.

Sections in this article:

• Introduction
• Non-Euclidean Geometry and Curved Space
• Elliptic Geometry
• Hyperbolic Geometry
• Bibliography

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