Proving the Parallelogram Side Theorem
Given: ABCD is a parellelogram.
Prove: AB=CD and BC=DA

Statements                                            Reasons

1. ABCD is a parallelogram                  1. Given

2. Seg. AB is parallel to seg. CD         2. Def of parallelogram

3. Seg. AD is parallel to seg. BC         3. Def of parallelogram

4. Draw seg. BD                                   4. Between 2 pts there is 1 line

5. <ABD is congr <CDB                        5. Alt. Int. < Theorem

6. <BDA is cong <DBC                         6. Alt. Int. < Theorem

7. Seg. BD is congr seg. BD                7. Congr. of seg's is reflexive

8. Triangle BAD is congr tr. DCB         8. SAS Postulate

9. AB is congr CD                                 9. CPCTC

10. BC is congr DA                                 10. CPCTC

11. AB = CD; BC = DA                           11. Def of congr. seg's

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