Geometry: Plane and Fancy

Abstract

1 Euclid and Non-Euclid.- 1.1 The Postulates: What They Are and Why.- 1.2 The Parallel Postulate and Its Descendants.- 1.3 Proving the Parallel Postulate.- 2 Tiling the Plane with Regular Polygons.- 2.1 Isometries and Transformation Groups.- 2.2 Regular and Semiregular Tessellations.- 2.3 Tessellations That Aren't, and Some Fractals.- 2.4 Complex Numbers and the Euclidean Plane.- 3 Geometry of the Hyperbolic Plane.- 3.1 The Poincare disc and Isometries of the Hyperbolic Plane.- 3.2 Tessellations of the Hyperbolic Plane.- 3.3 Complex numbers, Mobius Transformations, and Geometry.- 4 Geometry of the Sphere.- 4.1 Spherical Geometry as Non-Euclidean Geometry.- 4.2 Graphs and Euler's Theorem.- 4.3 Tiling the Sphere: Regular and Semiregular Polyhedra.- 4.4 Lines and Points: The Projective Plane and Its Cousin.- 5 More Geometry of the Sphere.- 5.1 Convex Polyhedra are Rigid: Cauchy's Theorem.- 5.2 Hamilton, Quaternions, and Rotating the Sphere.- 5.3 Curvature of Polyhedra and the Gauss-Bonnet Theorem.- 6 Geometry of Space.- 6.1 A Hint of Riemannian Geometry.- 6.2 What Is Curvature?.- 6.3 From Euclid to Einstein.- References.