Lesson objective: Determine if lines are parallel using angle relationships.

This lesson helps to build procedural skill with determining parallelism of lines. Game cards are used here because it highlights students' ability to recognize what an angle relationship tells us. This work develops students' understanding that the parallelism of lines can be determined by congruent angle relationships and lays a foundation for complex justification needed in more formal proofs and converses.

Students engage in Mathematical Practice 3 as they create valid arguments that two lines are parallel based on an angle relationship they are given and critique the reasoning of other students as they determine if their claims are justified as well. Students are also challenged to create their own clue cards for other students to justify.

**Key vocabulary:**

- alternate exterior angles
- alternate interior angles
- corresponding angles
- parallel lines
- transversal
- vertical lines

**Special materials needed:**