What is the relationship between an exterior angle in
a triangle and its corresponding remote interior angles. Why do you
think this relationship is true?
Click here to view this problem on Geometerís Sketchpad.† Grab point D and notice what happens to the sum of the interior angles of the triangle.† Notice what happens to the sum of the supplementary angles as you move it around.† Compare the sum of the two remote interior angles with the measure of the external angle as you move it around.†
What is the sum of the remote interior angles?† What is the measure of the exterior angle?†