Prove the Triangle Sum Theorem.
Given: Triangle ABC and lines d and f are parallel.
What is the measure of Angle A?
What is the measure of Angle B?
What is the measure of Angle C?
What is the measure of Angle BAF?
What is the measure of Angle CAG?
Angle BAF is congruent to Angle ______ because ___________.
Angle CAG is congruent to Angle ______ because ___________.
m<BAF + m<BAC + m<CAG = _______
What can you conclude about the sum of the angles in a triangle?