1. Introduction
Do the angles of a triangle add up to 180 degrees or radians.
For further reading see the article by Alan Beardon 'How many Geometries Are There?' and the article by Keith Carne 'Strange Geometries' . There are some practical activities that you can try for yourself to explore these geometries further to be found at http://nrich.maths.org/MOTIVATE/conf8/index.html