证明：延长BC到点F,使DF = DB
则：AD是BC的垂直平分线
∴AB =AF
∴∠B =∠F
∴ 2∠DAF = 2∠DAB = ∠BAF
∵∠ACB - ∠F = ∠FAC = ∠BAF - ∠BAC
= 2∠BAD - 2∠BAE =2（∠BAD - ∠BAE）= 2∠DAE
∴∠DAE = 1|2 （∠C - ∠B）