Question

What is the equation of a circle with center (9,-7) and radius 2?

A. (X - 9)2 + (y + 7)2 = 2
B. (X-9)2 + ( + 7)2 = 4
C. (x + 9)2 + (y - 7)2 = 2
D. (x + 9)2 + (x - 7)2 = 4

Answer 1

B. (x-9)^2 + (y + 7)^2 = 4

Explanation:

The standard form of a circle is (x-h)^2 + (y-k)^2 = r^2. Hopefully you can memorize that, because it's very helpful in these problems!

(h,k) is our center, and r is our radius, so plug those values into the standard form:

(x - 9)^2 + (y + 7)2 = 2^2

2^2 = 4, so

B. (x - 9)^2 + (y + 7)2 = 4 is our answer!