Given: a and b are parallel and c is a transversal. Prove: ∠2 ≅ ∠7 Use the drop-down menus to complete the paragraph proof showing that alternate interior angles are congruent. We know that lines a and b are parallel and that line c is a transversal because that is given. We can tell that angles 2 and 5 are congruent because angles are congruent. Angles 5 and 7 are congruent because angles by parallel lines cut by a transversal are congruent. Therefore, angles 2 and 7 are congruent based on the .