1.在Rt△ABC中,∠ACB=90°,AB=5,BC=3,將△ABC繞點(diǎn)B順時(shí)針旋轉(zhuǎn)得到△A'BC',其中點(diǎn)A,C的對(duì)應(yīng)點(diǎn)分別為點(diǎn)A',C'.
(1)如圖1,當(dāng)點(diǎn)A'落在AC的延長(zhǎng)線(xiàn)上時(shí),則AA'的長(zhǎng)為
;
(2)如圖2,當(dāng)點(diǎn)C'落在AB的延長(zhǎng)線(xiàn)上時(shí),連接CC',交A'B于點(diǎn)M,求BM的長(zhǎng);
(3)如圖3,連接AA',CC',直線(xiàn)CC'交AA'于點(diǎn)D,若AE=2,連接DE.在旋轉(zhuǎn)過(guò)程中,DE是否存在最小值?若存在,請(qǐng)直接寫(xiě)出DE的最小值:若不存在,請(qǐng)說(shuō)明理由.