A Saccheri Quadrilateral
A Saccheri quadrilateral, or Khayyam-Saccheri quadrilateral, is a four-sided figure. It has a base, AB, two equal legs standing at right angles to it, AC and BD, and non-obtuse angles at the summit, CD. It is composed entirely of straight lines.
It was discovered by Omar Khayyam and is named after Giovanni Gerolamo Saccheri. A rectangle is a special case of a Saccheri quadrilateral in which all four angles are right angles.
A Saccheri quadrilateral is composed of two equal Lambert quadrilaterals.
1. ^ a b Boris Abramovich Rozenfelʹd (1988), A History of Non-Euclidean Geometry: Evolution of the Concept of a Geometric Space, p. 65. Springer, ISBN 0387964584.
* George E. Martin, The Foundations of Geometry and the Non-Euclidean Plane, Springer-Verlag, 1975