Answer
ASA postulate
Work Step by Step
1. We know that segment AC is congruent to itself by the reflexive property.
2. We are given that AD is parallel to BC, and AB is parallel to DC.
3. We can use these sets of parallel lines and segment AC (the transversal) to determines congruent angles.
4. ∠BAC is congruent to ∠DCA, and ∠DAC is congruent to ∠BCA, by the alternate interior angles theorem.
5. So, now that we have two angles and a side that are congruent to the other triangle, we can conclude that △DAC is congruent to △BCA by the ASA (angle-side-angle) postulate.
