Exploring the Exterior Angle Theorem
Step 1: Please look at the first triangle and find the measure of angle ACD. Step 2: Please look at the same triangle and find the measure of angles B and A.
Step 3: Please look at triangle 2 and notice how the angles all change as you move point C along line BD. Step 4: What do you notice about the measure of angle ACD as it relates to angles A and B?
Step 5: This new triangle has no angle measures on it. Please write a rule that relates angles A and B to angle ACD and explain mathematically why it works. Hint: the interior angles of a triangle have a sum of 180 degrees as does the measure of a flat line. Step 6: Please give the measure of angle ACD without using numbers.