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Given: bc || de, and ∠gac ≅ ∠afd. prove: statement reason 1. ∠gac ≅ ∠afd given 2. ∠gac ≅ ∠afe for parallel lines cut by a transversal, corresponding angles are congruent. 3. 4. ∠afd and ∠afe are supplementary. linear pair theorem 5. m∠afd = m∠afe = 90° if two congruent angles are supplementary, then each angle is a right angle. 6. definition of perpendicular lines what is the missing step in the proof? a. statement: ∠gac and ∠gab are supplementary. reason: linear pair theorem b. statement: ∠afe ≅ ∠afd reason: transitive property of equality c. statement: ∠gac ≅ ∠baf reason: vertical angles theorem d. statement: ∠gac and ∠afd are supplementary. reason: linear pair theorem reset