Question x-4-2-

4.3 Circles - Equation of a circle in coordinate plane
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x+42+y-192=121

The graph of the given equation is a circle in the xy-plane. The point a,b lies on the circle. Which of the following is a possible value for a ?

A.

-16

B.

-14

C.

11

D.

19

x + 4 2 + y - 19 2 = 121 The graph of the given

Hard-difficulty · SAT Math · Circles — Equation of a circle in coordinate plane. Read the question above, select your answer, and check the full explanation below to understand exactly why the correct choice works.

Answer explanation

Choice B is correct. An equation of the form x-h2+y-k2=r2, where h , k , and r are constants, represents a circle in the xy-plane with center h,k and radius r . Therefore, the circle represented by the given equation has center -4,19 and radius 11 . Since the center of the circle has an x-coordinate of -4 and the radius of the circle is 11 , the least possible x-coordinate for any point on the circle is -4-11, or -15 . Similarly, the greatest possible x-coordinate for any point on the circle is -4+11, or 7 . Therefore, if the point a,b lies on the circle, it must be true that -15a7. Of the given choices, only -14 satisfies this inequality.

Choice A is incorrect and may result from conceptual or calculation errors.

Choice C is incorrect and may result from conceptual or calculation errors.

Choice D is incorrect and may result from conceptual or calculation errors.