Exterior Angles of Triangles

Front

What is an exterior angle of a triangle?

Back

An exterior angle of a triangle is formed by one side of the triangle and the extension of an adjacent side. It is equal to the sum of the two opposite interior angles.

Front

State 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 at the vertex of the 60° angle?

Back

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

Front

How do you find the measure of a missing angle in a triangle using exterior angles?

Back

To find a missing angle, use the Exterior Angle Theorem: the exterior angle equals the sum of the two opposite interior angles.

Front

What is the relationship between the sum of the interior angles of a triangle and the exterior angles?

Back

The sum of the interior angles of a triangle is always 180°, while the sum of the exterior angles is always 360°.

Front

If an exterior angle measures 130°, what are the measures of the two opposite interior angles?

Back

The two opposite interior angles must sum to 130°.

Front

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

Back

The measure of an exterior angle can be calculated as: Exterior Angle = Interior Angle 1 + Interior Angle 2.

Front

Can an exterior angle be less than either of the two opposite interior angles?

Back

No, an exterior angle is always greater than either of the two opposite interior angles.

Front

If a triangle has angles measuring 30°, 70°, and 80°, what is the measure of the exterior angle at the vertex of the 80° angle?

Back

The exterior angle is 30° + 70° = 100°.

Front

What happens to the measures of the exterior angles if the triangle is equilateral?

Back

In an equilateral triangle, each exterior angle measures 120° because each interior angle measures 60°.