Exterior Angle Theorem

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?

Back

The exterior angle is 100° (40° + 60°).

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

Solve for x: If one exterior angle is 120°, what are the measures of the two opposite interior angles?

Back

x = 60° and x = 60° (120° = 60° + 60°).

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 one angle of a triangle is 70° and another is 50°, what is the measure of the third angle?

Back

The third angle is 60° (180° - 70° - 50°).

Front

How do you find the measure of an exterior angle if you know the two opposite interior angles?

Back

Add the measures of the two opposite interior angles together.

Front

If an exterior angle measures 150°, what are the measures of the two opposite interior angles?

Back

The two opposite interior angles can be 75° and 75° (150° = 75° + 75°).

Front

What is the value of x if the exterior angle is 105° and one opposite interior angle is 45°?

Back

x = 60° (105° = 45° + x).

Front

If the exterior angle is 180°, what can you say about the triangle?

Back

The triangle is degenerate, meaning it collapses into a straight line.