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



ProveIt! by Michael Ferraro <mferraro@balstaff.org>.
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