Topic: Exterior Angle Theorem

Learning Objective:

• 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.

prior knowledge:

• 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.

procedure:

introduction/ motivation: students should be able to find the measurement of the exterior angle of the triangle.

two problems are given to the students.

1. find the measurement of angle A in the triangle abc with angle B = 50, angle C = 70?
2. 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.