A circle in the xy-plane has its center at and the point lies on the circle. Which equation represents this circle?
Correct answer: D
Explanation
Choice D is correct. A circle in the xy-plane can be represented by an equation of the form , where is the center of the circle and is the length of a radius of the circle. It's given that the circle has its center at . Therefore, and . Substituting for and for in the equation yields , or . It's also given that the point lies on the circle. Substituting for and for in the equation yields , or , which is equivalent to , or . Substituting for in the equation yields . Thus, the equation represents the circle.
Choice A is incorrect. The circle represented by this equation has its center at , not , and the point doesn't lie on the circle.
Choice B is incorrect. The point doesn't lie on the circle represented by this equation.
Choice C is incorrect. The circle represented by this equation has its center at , not , and the point doesn't lie on the circle.
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