证明:∵$AE$平分$∠BAD$
∴$∠BAC = ∠DAC$
∵$∠BCE + ∠ACB = 180°,$$∠DCE + ∠ACD = 180°,$$∠BCE = ∠DCE$
∴$∠ACB = ∠ACD$
在$\triangle ACB$和$\triangle ACD$中
$\begin {cases}∠BAC = ∠DAC \\AC = AC \\∠ACB = ∠ACD\end {cases}$
∴$\triangle ACB≌\triangle ACD(AS A)$
∴$AB = AD$