Lesson objective: Apply the triangle angle sum to polygons.

This lesson provides an opportunity for students to apply their knowledge and understanding of triangle angle sum to a mathematical situation. Students are asked to determine the interior angle sums of different polygons, analyze their results, and create a rule that determines the interior angle sum of any polygon.

Key Concept students will use:

- The angle sum for any triangle is 180 degrees, and we can informally prove this using the relationships of angles.

Skills students will use:

- angle sum of a triangle

Students engage in Mathematical Practice #3 (construct viable arguments and critique the reasoning of others) as they make conjectures about the polygon angle sum, justify their conclusions, and communicate them to others.

**Key vocabulary: **

- polygon
- triangle angle sum

**Special materials needed:**

- polygon templates (optional)