∫BC is the diameter of the circle O, and D is on the circle O.

∴∠BDC=90？

∴∠ADC= 190？ -∠BDC=90？

∴∠ADE+∠EDC=90？

DE perpendicular to AC at point e

∴∠ADE+∠A=90？

∴∠EDC=∠A

∠EDC=∠ABC

∴∠A=∠ABC

∴AC=BC

AB=AC

∴AB=AC=BC

∴ Triangle ABC is an equilateral triangle.