Lesson objective: Determine whether or not a transformation took place.

This lesson helps to build procedural skill with determining whether or not a transformation took place. Students learn to recognize that in order for a transformation to have taken place, the preimage and image must be congruent. This work develops students' understanding that side lengths and angle measurements stay the same when figures undergo a rigid transformation.

Students engage in Mathematical Practice 6 (Attend to Precision) as they carefully analyze figures and potential images to determine whether or not shapes are congruent and therefore to determine whether or not a specific transformation could have taken place.

**Key vocabulary:**

- angle
- congruent
- line
- ray
- reflection
- rotation
- segment
- translation

**Special materials needed:**

- protractors (optional)
- rulers (optional)

Note: Students may want to use rulers and/or protractors when determining whether or not shapes are congruent. These tools are useful, but not necessary to master the lesson objective.