Journal of the Mathematics Council of the Alberta Teachers’ Association
Volume 41 Issue 2, June 2004
4 – 9
Determining the Angles Between Two Lines
David E. Dobbs
In preparing a recent lecture for a course on non-Euclidean geometry, I needed a formula to determine the angles formed by two intersecting lines in Euclidean plane geometry. The relevant formulas in Proposition 6.2 of The Poincare Half Plane: A Gateway to Modern Geometry (Stahl 1993), the textbook for the course, depended on methods not needed again until the textbook’s coverage of the hyperbolic version of the Pythagorean theorem (Theorem 8.3). I decided to seek alternative formulas with minimal prerequisites and the additional benefit of being easy to implement on modem calculators
