∴ACED is a parallelogram,
∴AC=DE,
∵ isosceles trapezoid ABCD,
∴AC=BD,
∴BD=DE?
∵AC⊥BD,
∴∠BOC=90,
∫AC∑DE,
∴∠BOC=∠BDE=90,
∴△BDE is an isosceles right triangle.
(2) solution: ∫AD∨BC,
∴OAOC=ODOB=ADBC,
∴ACOC=BDOB
∵ isosceles trapezoid ABCD,
∴AC=BD,
∴OC=OB,OA=OD,
∫DE∑AC,
∴∠CDE=∠DCO,
∴sin∠CDE=sin∠DCO=55,
At Rt△DCO, let OD=k and DC=5k? (k > 0), then OC=DC2? OD2=2k,
Parallelogram ACDE,
∴AD=CE,
∴ODOB=ODOC= 12,
∴ADBC= 12,
∴ADBE= 13.