(1)易证△AOD~△COB △BOE~△BDA △COF~△CAD
∴CO/AO=BO/DO 合比性质可得CO/AC=BO/BD
∵OB/BD=OE/AD OC/AC=OFAD
∴OE/AD=OF/AD
∴OE=OF
(2)由(1)可得OB/OD=BC/AD=4/3
∴OE/AD=OB/BD=4/7
OE/3=4/7 OE=12/7
∴EF=2OE=24/7
(1)易证△AOD~△COB △BOE~△BDA △COF~△CAD
∴CO/AO=BO/DO 合比性质可得CO/AC=BO/BD
∵OB/BD=OE/AD OC/AC=OFAD
∴OE/AD=OF/AD
∴OE=OF
(2)由(1)可得OB/OD=BC/AD=4/3
∴OE/AD=OB/BD=4/7
OE/3=4/7 OE=12/7
∴EF=2OE=24/7