Answer:
AB ║ CD, reason If two lines (AB and CD) and a transversal AD, form alternate interior angles, (∠1 and ∠4) that are congruent, then the two lines are parallel
Step-by-step explanation:
Statement, Reason
Triangle ACD is isosceles, Given
∠1 ≅ ∠3, Given
∠3 ≅ ∠4, Base angles of isosceles triangle
∠1 ≅ ∠4, Substitution
∠1 and ∠4, are alt int. ∠s, Definition
AB ║ CD, Have congruent alternate interior angles
If two lines (AB and CD) and a transversal AD, form alternate interior angles, (∠1 and ∠4) that are congruent, then the two lines are parallel
