1. The document discusses the exterior angle property of triangles, which states that the exterior angle of a triangle is equal to the sum of its two opposite interior angles. 2. To demonstrate this, students are instructed to cut out triangles from different colored paper, name the angles, and place the interior angles adjacent to each other to show they cover the exterior angle. 3. By observing this activity, students can infer that the measure of the exterior angle is equal to the sum of the measures of its two opposite interior angles.