Paper 2, Section I, F

Geometry of Group Actions
Part II, 2010

Show that a map T:R2R2T: \mathbb{R}^{2} \rightarrow \mathbb{R}^{2} is an isometry for the Euclidean metric on the plane R2\mathbb{R}^{2} if and only if there is a vector vR2\boldsymbol{v} \in \mathbb{R}^{2} and an orthogonal linear map BO(2)B \in \mathrm{O}(2) with

T(x)=B(x)+v for all xR2T(\boldsymbol{x})=B(\boldsymbol{x})+\boldsymbol{v} \quad \text { for all } \boldsymbol{x} \in \mathbb{R}^{2}

When TT is an isometry with detB=1\operatorname{det} B=-1, show that TT is either a reflection or a glide reflection.