I am reading Grove and Benson's book on Finite Reflection Groups and am struggling with some of the basic linear algebra.
Some terminology from Grove and Benson:
V is a real Euclidean vector space
A transformation of V is understood to be a linear transformation
The group of all orthogonal transformations of V will be denoted O(V)
Then in chapter 2, Grove and Benson write the following:
If T [TEX]\inEX] O(V), then T is completely determined by its action on the basis vectors = (1,0) and = (0,1).
If T , then and
Can someone please help by proving why the last statement is true?