Rigidity of angles in Inner product Spaces

Abstract

In this article, we discuss the equality of two inner products on a vector space. Particularly, we look at some geometric properties that are given to a vector space by an inner product namely, length and angle, and we ask under what conditions on these geometric properties do two inner products coincide. Some parts of this article can be found as exercise problems in various books on geometry. We give a slight generalization to these exercises and exposit the rigid nature of angles in an inner product space.