∵AB = CD
∴∠ABC = ∠DCB
∵AD = DC
∴∠DAC = ∠DCA
∵AD//BC
∴∠DAC = ∠ACB
∴AC是∠DCB的角平分线
∵∠ABC = ∠DCB
∴∠ABC :∠ACB = 2:1
∵AC ⊥ AB
∴∠ABC = 60°,∠ACB = 30°
∵AB = CD
∴∠ABC = ∠DCB
∵AD = DC
∴∠DAC = ∠DCA
∵AD//BC
∴∠DAC = ∠ACB
∴AC是∠DCB的角平分线
∵∠ABC = ∠DCB
∴∠ABC :∠ACB = 2:1
∵AC ⊥ AB
∴∠ABC = 60°,∠ACB = 30°