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Okay, so in problem at the top of the page, the center is (-13,-16) and a point on the circle is (-10,-16). So I understand I need to use the distance formula. Would -13 be x1, -16 be y1, -10 be x2 and -16 be y2? Why does it seem to me like the numbers are not in their correct spots in the distance formula? This is driving me nuts!