Explanation:
2. AB || CD 2. Def of parallelogram
3. <BAC is congr <DCA 3. alt int angles of parallel lines
4. seg AB is congr seg CD 4. Theorem: opp sides of parallel are congr
5. <s AEB and CED are rt <s 5. Def of perpendicular lines
6. <AEB is congr <CED 6. Theorem: all right angles are congr
7. tr. AEB is congr tr. CED 7. AAS
8. seg. AE is congr seg. CE 8. CPCTC
9. <BEC is a rt < 9. Def of perpendicular lines
10. <AEB is congr <BEC 10. Theorem: all right angles are congr
11. seg BE is congr seg. BE 11. Theorem: congr of seg's is reflexive
12. tr. AEB is congr tr. CEB 12. SAS
13. seg AB congr seg BC 13. CPCTC