∵四边形ABCD中,AB=DC,AC=DB,BC=BC,∴△ABC≌△DCB,∴∠ABC=∠DCB.
同理得∠BAD=∠CDA.
∵∠ABC+∠BCD+∠CDA+∠BAD=360,∴2(∠BAD+∠ABC)=180,∴AD‖BC.
∵AD不等于BC,∴四边形ABCD是梯形.∵ AB=DC,∴四边形ABCD是等腰梯形.
∵四边形ABCD中,AB=DC,AC=DB,BC=BC,∴△ABC≌△DCB,∴∠ABC=∠DCB.
同理得∠BAD=∠CDA.
∵∠ABC+∠BCD+∠CDA+∠BAD=360,∴2(∠BAD+∠ABC)=180,∴AD‖BC.
∵AD不等于BC,∴四边形ABCD是梯形.∵ AB=DC,∴四边形ABCD是等腰梯形.