Question

Which equation represents a circle with a center at (–4, 9) and a diameter of 10 units?

(x – 9)2 + (y + 4)2 = 25
(x + 4)2 + (y – 9)2 = 25
(x – 9)2 + (y + 4)2 = 100
(x + 4)2 + (y – 9)2 = 100

Answer 1

Radius = diameter/2 = 5, so r^2 = 25. With center (h,k) = (−4,9) the circle is (x − (−4))^2 + (y − 9)^2 = 25, i.e. (x + 4)^2 + (y − 9)^2 = 25.