Question

Which is an equation of the circle with a radius of 9 units and center at

(–4, 2)?
A.
(x − 9)2 + (y + 4)2 = 4
B.
(x − 4)2 + (y + 2)2 = 81
C.
(x + 4)2 + (y − 2)2 = 81
D.
(x − 2)2 + (y + 4)2 = 81

Answer 1

We want (x - h)^2 + (y - k)^2 = r^2.

This circle is not centered at the origin.

The point we want is in the form

(h, k).

We are given that h = -4 and k = 2.

We also know that the radius is 9.

Let r = 9 leading to (9)^2 or 81.

We know substitute in the form given above for circles not centered at the origin.

(x - (-4)^2 + (y - 2)^2 = 81

(x + 4)^2 + (y - 2)^2 = 81

Answer: Choice C