Exterior Angle Theorem - Triangles

Front

What is the Exterior Angle Theorem?

Back

The Exterior Angle Theorem states that the measure of an exterior angle of a triangle is equal to the sum of the measures of the two non-adjacent interior angles.

Front

If one interior angle of a triangle is 40° and another is 60°, what is the measure of the exterior angle adjacent to the 60° angle?

Back

The exterior angle is 40° + 60° = 100°.

Front

What is the relationship between an exterior angle and its adjacent interior angle?

Back

The exterior angle is equal to the sum of the two opposite interior angles, not the adjacent one.

Front

In triangle ABC, if angle A = 50° and angle B = 70°, what is the measure of angle C?

Back

Angle C = 180° - (50° + 70°) = 60°.

Front

If angle A = 30° and angle B = 90°, what is the measure of the exterior angle at vertex A?

Back

The exterior angle at vertex A = 90° + 30° = 120°.

Front

How do you find the measure of an unknown angle in a triangle using the Exterior Angle Theorem?

Back

Add the measures of the two non-adjacent interior angles to find the measure of the exterior angle.

Front

What is the sum of the interior angles of a triangle?

Back

The sum of the interior angles of a triangle is always 180°.

Front

If an exterior angle measures 130°, what are the possible measures of the two non-adjacent interior angles?

Back

The sum of the two non-adjacent interior angles must equal 130°.

Front

In triangle DEF, if angle D = 45° and angle E = 55°, what is the measure of angle F?

Back

Angle F = 180° - (45° + 55°) = 80°.

Front

What is the formula to calculate the measure of an exterior angle?

Back

Exterior Angle = Interior Angle 1 + Interior Angle 2.