∫BE is the diameter of the circle o.
∴∠BAE=90
∵AB⊥CD
∴AE∥CD
∴ Quadrilateral AECD is a trapezoid.
∫ arc AE= arc AE
∴∠ACD=∠ADC
∴ Trapezoidal AECD is an isosceles trapezoid.
∴AC=ED
AC = 3
∴DE=3