In this lesson, students are challenged to identify missing information needed to define a reflection by engaging in an Information Gap activity. There is an optional activity which briefly returns to the structure of a grid to determine whether the order of transformations impacts the final image. In the Lesson Synthesis, students record the rigorous definition of a reflection as a transformation that takes every point of a figure to a point directly opposite to it on the other side of the line of reflection and the same distance from the line of reflection.

The Information Gap activity might take longer than expected since it's the first one in the course. Engaging in the process of requesting information without knowing what questions to ask will require perseverance (MP1).

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.

Math Community

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.