Proof: Converse of Parallel Lines 4     
line ABCD
ECD = 140
ABF = 40
line BF line CE
1. 
1. 
ABC = ABF + FBC
FBC = FBC
ECD = 140
BCD = BCE + ECD
140 = FBC
line ABCD
FBC + BCE = 140 + 40; FBC + BCE = 180
FBC and BCE are supplementary
line BF line CE
FBC + BCE = FBC + BCE
180 = 40 + FBC
ABF = 40
180 = BCE + 140
40 = BCE
ABC = 180
BCD = 180



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