1、连结BD、AO,
∵AF=BF,
∴OF⊥AB,
RT△DAF≌RT△DFB,
〈DAF=〈FBD,
〈ABD=〈ACD(同弧圆 周角相等),
〈ACD=〈DAE,
〈ADC=〈CDA(公用),
∴△DAC∽DEA.
2、OA=OD=3,AF=√5,
根据勾股定理,OF=2
DF=,
AD=√(DF^2+AF^2)=√30.
△DAC∽DEA,
AD/CD=DE/AD,
AD^2=DE*CD,
DE*CD=30,.(1)
AB=BE=2√5,AE=4√5,
而根据割线定理可知,
CE*DE=BE*AE=2√5*4√5=40,.(2),
(1)+(2),
DE*(CD+CE)=70,
DE^2=70,
DE=√70,
CE=4√70/7,
CD=3√70/7,
AC/AE=AD/DE,
AC=4√105/7.