
 Amazon.com: Geometry: Books: David A. Brannan,Matthew F. Esplen,Jeremy J. Gray (Site not responding. Last check: 20070917) 
  During the last third of the book (the chapters on hyperbolic and spherical geometry), some basic familiarity with trigonometric functions and hyperbolic functions is assumed (cosh, sinh, tanh, and their inverses). 
  In the eighth chapter all of these geometries are demonstrated to be special cases of the Kleinian vieuw of geometry: that is, every geometry can be seen as consisting of the invariants of a specific group of transformations of the 2 dimensional plane into itself. 
  And, by passing to the more abstract Projective geometry, you can express the abstract idea of 'conic' by giving just one quadratic curve, be it a parabola, ellipse or hyperbola, by the pair (Qu, P), whereby P is the group of all projective transformations. 
 www.amazon.com /GeometryDavidBrannan/dp/0521597870 (2910 words) 
