Solution: Angle AOC is the central angle of arc AC, and angle B is the central angle of arc AC.
∴ Angle B= 1/2 Angle AOC = 6 1■
∵ The quadrilateral ABCD is inscribed in the circle O, so the angle B+ the angle ADC = 180.
∴ADC = 180-6 1 = 1 19。
EDC = ADE-ADC = 180- 1 19 = 6 1。
To sum up: angle B= angle EDC = 6 1.
In fact, there is a conclusion: the outer angle of each corner of the inscribed quadrangle of a circle is equal to the angle opposite to this angle.
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