Question 384558: Parallelogram ABCD is inscribed in circle O. Find the measure of angle A.
Answer by richard1234(7193)   (Show Source):
You can put this solution on YOUR website! By definition, if the parallelogram is inscribed in a circle, it is cyclic, and the measures of opposite angles add up to 180 (i.e. A + C = 180, B + D = 180). However, ABCD is a parallelogram, so A + B = 180, B + C = 180, etc. It follows that A = B, B = C, etc, so ABCD is a rectangle, and angle A = 90 degrees.
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