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

If the measures of two interior angles of a triangle are 70° and 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 one of the interior angles?

Back

You can find the exterior angle by adding the measures of the two non-adjacent interior angles.

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 120°, what are the possible measures of the two non-adjacent interior angles?

Back

The sum of the two non-adjacent interior angles must equal 120°.

Front

In a triangle, if one exterior angle is 135°, what is the sum of the two opposite interior angles?

Back

The sum of the two opposite interior angles is 135°.

Front

What is the measure of an exterior angle if one of the non-adjacent interior angles is 45° and the other is 55°?

Back

The exterior angle measures 100° (45° + 55°).

Front

If an exterior angle is 180°, what does that imply about the triangle?

Back

An exterior angle of 180° implies that the triangle is degenerate (the points are collinear).