Final answer:
By using the properties of parallel lines and the ASA Postulate, we can prove that triangle ABD is congruent to triangle DCA due to congruent alternate interior angles and a shared side.
Step-by-step explanation:
We are given that AC is parallel to BD, and CD is parallel to AB. Since AC is parallel to BD, and they are both intersected by AD, the alternate interior angles formed are congruent. That means ∠CAD is congruent to ∠BDA. Similarly, since CD is parallel to AB, and they are intersected by AD, the alternate interior angles formed are congruent as well. Hence, ∠ACD is congruent to ∠BAD. By the Reflexive Property of Equality, AD is congruent to AD. With two pairs of congruent angles and a common side, △ABD is congruent to △DCA by the ASA Postulate (Angle-Side-Angle).