Prove: ABCD is a parallelogram. E A B D C Statements Reasons 1. AB = CD;AD = BC 1. given 2. AC = AC 2. reflexive property 3. AADC - ACBA 3.? 4. ZDAC = ZBCA; ZACD = Z CAB 4. CPCTC 5. ZDAC and ZBCA are alt. int. Zs; 5. definition of alternate interior angles ZACD and ZCAB are alt. int. Zs 6. AB // CD; AD // BC 6. converse of the alternate interior angles theorem 7. ABCD is a parallelogram 7. definition of parallelogram What is the missing reason in step 3? ​