se the results of Section 3.7 to show that each member of Isom+(R^2) is either a translation or a rotation. Why does an isometry map any circle to a circle? We took care to write the inverse of the isometry r_1r_2r_3 as r_3r_2r_1 because only this ordering of terms will always give the correct result. Give an example of two reflections r_1 and r_2 such that r_1r_2 = r_2r_1.