延长AE到F,使EF＝AE,连结DF.因为EF＝AE,DE＝EC,角AEC＝角DEF,则三角形AEC全等于三角形DEF,所以DF＝AC,角ACE＝角CDF,又因为AD是中线,AC=1/2BC,所以DF＝AC＝DC＝BD,所以角CAD＝角ADC,加上刚才证的角ACE＝角CDF可以得到角ADB＝角ADF,已经证了DF＝BD,AD是公共边,所以三角形ADB全等于三角形ADF,所以角BAD＝角FAD,即AD平分角BAE