You are right. In circle equation we have =r² so the correct answer will be C od D. But we have to calculate the center of a circle.

Complete the square:

And we have:

So the answer is C (the same left side of equation).
<span>It can be assumed that the sample mean would would be approximately normal by the mean distribution theorem. The mean distribution theorem states that a large enough sample size will have a distribution and mean approximately the same as the population mean. A sample of 250, half the size of 500, is of sufficient size to assume the distribution mean will be approximately normal like the population mean.</span>