The purpose of this lesson is for students to observe properties of figures that have been rotated 90 degrees or 180 degrees. They generalize that a line segment rotated 180 degrees about a point is either parallel to the original or lies along the same line (MP8). They also identify rigid transformations on a triangle involving rotations of multiples of 90 degrees. Students explain that lengths on the composite figure must be equal using the property of rigid transformations that corresponding side lengths are the same (MP3).  The composite figure in this activity arises in a later unit to support thinking about the Pythagorean theorem.

Today, students use sticky notes to document actions in the “Doing Math” sections of the Math Community Chart that they see or hear throughout the lesson. During the Lesson Synthesis, students share what they noticed, and then they suggest additions for the chart as part of the Cool-down. The work today continues to build a foundation for developing math community norms in a later exercise and is the start of students identifying strengths in the actions of their peers.