3.如圖,△ABC中,AB=AC=2,∠B=40°.點(diǎn)D在線段BC上運(yùn)動(dòng)(點(diǎn)D不與B、C重合),連接AD,作∠ADE=40°,DE交線段AC于E.
(1)當(dāng)∠BAD=20°時(shí),∠EDC=
°;
(2)當(dāng)DC等于多少時(shí)△ABD≌△DCE?并說(shuō)明理由;
(3)在點(diǎn)D的運(yùn)動(dòng)過(guò)程中,△ADE的形狀也在改變,判斷當(dāng)∠BAD等于多少度時(shí),△ADE是等腰三角形.