Transforming Angles

This lesson focuses on the effects of rigid transformations on lines and angles. In particular, students see that parallel lines are taken to parallel lines under any rigid transformations. Rigid transformations are used to justify that pairs of vertical angles and alternate interior angles on parallel lines are congruent.

By Desmos Classroom

Learning goals: Learning Goals • Understand that lines are taken to lines and parallel lines are taken to parallel lines under rigid transformations. • Establish the vertical angle theorem through informal arguments. • Identify congruent angles on two parallel lines cut by a transversal and use them to determine missing angle measurements. Materials • Geometry toolkits (particularly tracing paper and a straightedge) • Blank paper