解:∠ABC的平分线交CD于点E,则∠ABE=∠CBE.∠ADC的平分线交AB于点F,则∠ADF=∠CDF.又∠ABC=∠ADC.即∠ABE=∠CBE=∠ADF=∠CDF.因为AB交BE,DF于B,F两点,且∠ABE=∠ADF所以BE平行于FD.(同位角相等,两直线平行).因为BF平...