Topic: Exterior Angle Theorem
- The students will be able to explain verbally and in writing the relation between the exterior and the interior angles of the triangle
- the students will be able to find the measurement of the exterior angle of the triangle or one of the interior angles.
CCSS Standards: 8.G.5
Use informal arguments to establish facts about the angle sum and exterior angle of triangles, about the angles created when parallel lines are cut by a transversal, and the angle-angle criterion for similarity of triangles.
Instructional resources and materials: smart board and computer with Geogebra.
key vocabulary: exterior angle, interior angle.
- the students should be familiar with straight angle and it’s measurement, and supplementary angles.
- the students should know the total measurements of the interior angles of the triangle.
focus idea or questions: what is the relationship between the exterior and the interior angles of the triangle.
introduction/ motivation: students should be able to find the measurement of the exterior angle of the triangle.
two problems are given to the students.
- find the measurement of angle A in the triangle abc with angle B = 50, angle C = 70?
- find the measurement of the
time estimate: 10 minutes
instructional strategies and learning activities: Geogebra sheet is given to the students.
practice: the students have to follow the instruction in the Geogebra sheet.
closure: the students are given an exit slip with one question to reflect on how helpful was Geogebra in understanding how the exterior angle and the interior angle are related.