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



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