As shown in the figure, four points a, F, C and D are known to be on the same straight line, AF = CD, ab ‖ BC and ef ‖ BC. The formula shows that (1) △ ABC ≌ △ def; (2) angle CBF = angle FEC

As shown in the figure, four points a, F, C and D are known to be on the same straight line, AF = CD, ab ‖ BC and ef ‖ BC. The formula shows that (1) △ ABC ≌ △ def; (2) angle CBF = angle FEC

(1) ∵ AB / / de ∵ EDF = ∵ BAC ∵ EF / / BC ∵ EFD = ∵ BCA ∵ AF = DC ∵ AF + FC = FC + CD ∵ AC = DF ∵ EDF = ∵ bacdf = AC ? EFD = ? BCA ≌ ABC ≌ def (corner and corner) (2): ? ABC ≌ def ≌ BC = EF, ≌ EFC = ≌ BCF ∵ BC = EF ∵ EFC = ≌ bcfcf = CF ≌ CFE