Geometry aids in our perception of the world. We can use it to deconstruct our view of objects into lines and circles, planes and spheres. For example, some properties of triangles that we know are that it consists of three straight lines and three angles that sum to π. Can we imagine other geometries that do not give these familiar results? The Euclidean geometry that we are familiar with depends on the hypothesis that, given a line and a point not on that line, there exists one and only one line through the point parallel to the line. This is one way of stating Euclid’s parallel postulate. Since it is a postulate and not a theorem, it is assumed to be true without proof. If we alter that postulate, new geometries emerge.
This paper explores one model of that Non-Euclidean Geometry-the Poincar ́e model of Hyperbolic Geometry. We will explore the Poincar ́e model, based on a system of orthogonal circles (circles which interesect each other at right angles), and learn about some of its basic aspects. Then we will study the characteristics of triangles in this geometry through discovering relationships between parts of triangles and deriving hyperbolic forms of the Pythagorean Theorem and the Laws of Sines and Cosines. While doing so we will also come across the concepts of Inversion and Radical Axes. First, however, we will have a brief review of the history leading up to the development of the Poincar ́e model.