An account of how axioms underpin geometry and how by changing one axiom we get an entirely different geometry.
Prove Pythagoras' Theorem for right-angled spherical triangles.
This article outlines the underlying axioms of spherical geometry giving a simple proof that the sum of the angles of a triangle on the surface of a unit sphere is equal to pi plus the area of the. . . .
How do we measure curvature? Find out about curvature on soccer and rugby balls and on surfaces of negative curvature like banana skins.