Lesson 13

This lesson continues to build on prior knowledge about congruence to reinforce the idea that the rigid motions, translations, reflections, and rotations preserve distances and angles. In this lesson, students return to studying transformations on a grid, as they encounter rotations for the first time in this course. In subsequent lessons in this unit, students learn a precise definition for rotation that applies off the grid. 

In one activity, students complete a sequence of translation, reflection, and rotation where each rigid motion lines up one pair of points in a pair of congruent triangles. This sequence of point-by-point transformation will be the basis for triangle congruence proof in a subsequent unit. Students attend to precision when they determine the necessary pieces of information to describe a rotation as well as when they determine appropriate levels of confidence when measuring with a protractor (MP6).

Note that these materials use the convention that all named angles are assumed to measure less than 180 degrees, unless otherwise specified.

Technology isn't required for this lesson, but there are opportunities for students to choose to use appropriate technology to solve problems. We recommend making technology available.