Exterior Angle Theorem

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.

To calculate the measure of an exterior angle, add the measures of the two opposite interior angles.

The exterior angle is 40° + 70° = 110°.

The sum of the measures of the interior angles of a triangle is always 180°, and each exterior angle is equal to the sum of the two opposite interior angles.

Angle C = 180° - (50° + 60°) = 70°.

The sum of the exterior angles of any polygon is always 360°, regardless of the number of sides.

The exterior angle at vertex Z is 30° + 50° = 80°.

You can find a missing angle by using the formula: Missing angle = Exterior angle - adjacent interior angle.

The measure of the exterior angle is 45° + 55° = 100°.

The two opposite interior angles must sum to 120°; for example, they could be 60° and 60° or 70° and 50°.