A circle has a diameter with endpoints at 5 + 18i and –3 + 2i. What is the center of the circle?

The center is the midpoint of the diameter’s endpoints. Average their real parts and imaginary parts separately: (5 + (−3))/2 = 1 and (18 + 2)/2 = 10. So the center is 1 + 10i, choice B.

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