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D B G A E C F In the figure above, DE is parallel to GF . Find a way to prove that the angles in ABC have a sum of 180. D B G A E C F In the figure above, DE is parallel to GF . Find a way to prove that the angles in ABC have a sum of 180. Statement Reason 1. Given 1. 2. Alternate Interior Angles Theorem 2. 3. 3. Reflexive Property of Congruence 4. 4. Definition of Congruency 5. is a straight angle 5. Picture 6. 6. Definition of a Straight Angle 7. 7. Angle Addition Postulate 8. 8. Substitution