It is known that, as shown in the figure, angle ABC = angle DCB, BD and Ca are the bisectors of angle ABC and angle DCB respectively

It is known that, as shown in the figure, angle ABC = angle DCB, BD and Ca are the bisectors of angle ABC and angle DCB respectively


Connect ad ∵ BD and Ca to divide ∵ ABC and ∵ DCB ∵ ABO = ∵ OBC, ∵ DCO = ∵ OCB ∵ ABC = ∵ DCB ≌ ABC - ≌ ABO = ≌ DCB - ≌ DCO, that is