Students will learn why the opposite angles of a parallelogram are congruent. Before attempting to understand the proof, students should know the SSS congruence theorem and that corresponding parts of congruent triangles are congruent.

Conclude by giving your students these challenges:

- Cutting it Out by NRICH
- Seven Squares - Group-worthy Task by NRICH
- X Marks the Spot by NRICH
- 2010 AMC 8, Problem 11