3.已知,在?ABCD中,AB⊥BD,AB=BD,E為射線BC上一點(diǎn),連接AE交BD于點(diǎn)F.
(1)如圖1,若點(diǎn)E與點(diǎn)C重合,且AF=2
,求AD的長;
(2)如圖2,當(dāng)點(diǎn)E在BC邊上時,過點(diǎn)D作DG⊥AE于G,延長DG交BC于H,連接FH.求證:AF=DH+FH;
(3)如圖3,當(dāng)點(diǎn)E在射線BC上運(yùn)動時,過點(diǎn)D作DG⊥AE于G,M為AG的中點(diǎn),點(diǎn)N在BC邊上且BN=1,已知AB=4
,請直接寫出MN的最小值.