∫ In trapezoidal ABCD, AD∨BC,
∴∠EAD=∠B,
In △DEA and △ABC,
AE=BC∠EAD=∠BAD=AB,
∴△DEA≌△ABC(SAS),
∫∠AED =α,
∴∠BCA=∠AED=α,
AD = CD,
∴∠DCA=∠DAC=∠ACB=α,
∴∠bcd=∠dca+∠acb=2α;
(2) Ed ∠BEC,
∴∠AEC=2∠AED=2α.
∫ ABCD, AD∨BC, AB=CD in the trapezoid,
∴∠EAD=∠B=∠BCD=2α=∠AEC,
∴CE=BC=AE,
∴∠ECA=∠EAC=∠EAD+∠DAC=3α,
∴∠ECB=∠ECA+∠ACB=4α.
∵∠B+∠BEC+∠BCE= 180,
∴2α+2α+4α= 180 ,
∴∠ECB=4α=90。
∴△EBC is an isosceles right triangle.