In this activity, students will measure interior and exterior angles of a triangle and make conjectures about their relationships.

Students construct a triangle and measure the three interior angles. With the Text and Calculate tools they make a conjecture about the sum of the angles for all triangles, acute, obtuse, and right.

Using a pre-constructed triangle, students will construct a line and measure the exterior angle that results from it. Using manual data capture and the Lists & Spreadsheet application, they will make conjectures about the relationships of interior and exterior angles.

On a Graphs & Geometry page, students will use rays to construct the exterior angles of a triangle. They will use the Text and Calculate tools again to make a conjecture about the sum of the angles. Additional problems are given in the teacher document for students to apply what they have learned in the activity.