U1L20 Transformations, Transversals, and Proof

In this lesson, students use rigid transformations to understand the angle relationships formed by parallel lines and a transversal. This is the beginning of transformation proof, an important theme of subsequent units. By forming parallel lines with a translation students see corresponding angles are congruent. Then they form parallel lines with a 180 degree rotation and see alternate interior angles are congruent. These experiences prepare students to choose a sensible translation or rotation when they prove that parallel lines cut by a transversal have alternate interior angles that are congruent and corresponding angles that are congruent in the cool-down. Students attend to precision when they use the definitions, theorems, and assertions about translations and rotations to explain why the images of certain objects are guaranteed to coincide with other objects (MP6). This activity includes lesson summary videos and practice problems.

By JOEL NELSON