This is high school Given: g ∥ h and ∠2 ≅ ∠3 Prove: e ∥ f Horizontal and parallel lines e and f are intersected by diagonal and parallel lines g and h. At the intersection of lines g and e, the bottom right angle is angle 2. At the intersection of lines h and e, the bottom right angle is angle 1. At the intersection of lines f and h, the top left angle is angle 3. Statements Reasons 1. g || h 1. given 2. ∠1 ≅ ∠2 2. corresponding angles theorm 3. ∠2 ≅ ∠3 3. given 4. ∠1 ≅ ∠3 4. transitive property 5. e || f 5. ? What is the missing reason in the proof? vertical angles theorem alternate exterior angles theorem converse corresponding angles theorem converse alternate interior angles theorem