# Exterior Angle Theorem

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Examples, solutions, videos, worksheets, games and activities to help Geometry students learn about the Exterior Angle Theorem.
How to define the interior and exterior angles of a triangle?
How to solve problems related to the exterior angle theorem using Algebra?

The following diagram shows the exterior angle theorem. Scroll down the page for more examples and solutions involving the exterior angle theorem.

Exterior Angles
If one side of a triangle is extended beyond the vertex, an exterior angle is formed. This exterior angle is supplementary with its adjacent, linear angle. Since the angle sum in a triangle is also 180 degrees, the exterior angle must have a measure equal to the sum of the remaining angles, called the remote interior angles.

How to define exterior angles and their remote interior angles and how to prove their properties.
Introduction to the Interior and Exterior Angles of a Triangle
This video will define the interior and exterior angles of a triangle and then state several theorems involving the interior and exterior angles of a triangle.

Exterior Angle Theorem
This video explains the exterior angle theorem of geometry. The theorem is used to work out some applications in finding angles of a triangle.

The Exterior Angle Theorem
Students learn the exterior angle theorem, which states that the exterior angle of a triangle is equal to the sum of the measures of the remote interior angles. Students are then asked to solve problems related to the exterior angle theorem using Algebra.

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