Grade 8 Geometry: Angle Relationships

Worked examples

Real problems from the practice worksheets, solved one step at a time.

1. Example 1

   Two parallel lines are cut by a transversal. One interior angle measures 49°. What is the measure of its alternate interior angle, in degrees?

   1. When parallel lines are cut by a transversal, alternate interior angles are equal.
   2. So the alternate interior angle measures 49°.

   Answer: 49

2. Example 2

   Two interior angles of a triangle measure 43° and 39°. What is the measure of the exterior angle at the third vertex, in degrees?

   1. An exterior angle of a triangle equals the sum of the two interior angles that are not next to it.
   2. 43° + 39° = 82°.

   Answer: 82

3. Example 3

   An exterior angle of a triangle measures 80°. One of the two interior angles not next to it measures 40°. What is the measure of the other one, in degrees?

   1. An exterior angle of a triangle equals the sum of the two interior angles that are not next to it.
   2. 80° − 40° = 40°.

   Answer: 40