In previous lessons, students identified and described lines, line segments, rays, and angles in geometric and real-world contexts. The purpose of the exploratory work in this lesson is for students to make sense of which attributes define an angle (rays at a common starting point) and which attributes do not (lengths of the line segments). The activities in the lesson intentionally elicit students’ ideas for how to describe an angle’s size.

Throughout the lesson, monitor for the ways students distinguish visible line segments from the rays that compose the angles, and the language they use to describe the size of an angle.