∵AD//BC
∴∠ADB = ∠DBC
∵AB = AD
∴∠ADB = ∠ABD
∴∠ABD = ∠DBC
∵AB = CD
∴∠ABC = ∠C
∴∠DBC = ∠C/2
∵BD⊥CD
∴∠DBC = 30°,∠C = 60°
∴BC = 2CD
∵AD//BC
∴∠ADB = ∠DBC
∵AB = AD
∴∠ADB = ∠ABD
∴∠ABD = ∠DBC
∵AB = CD
∴∠ABC = ∠C
∴∠DBC = ∠C/2
∵BD⊥CD
∴∠DBC = 30°,∠C = 60°
∴BC = 2CD