Question #N77
A circle in the $xy$-plane has center $(1,2)$ and radius 3. Which of the following is an equation of the circle?
A. (x + 1)^2 + (y + 2)^2 = 3
B. (x - 1)^2 + (y - 2)^2 = 3
C. (x - 1)^2 + (y - 2)^2 = 9
D. (x + 1)^2 + (y + 2)^2 = 9
Correct Answer is: C
The standard form of the equation of a circle with center $(h,k)$ and radius $r$ is $(x - h)^2 + (y - k)^2 = r^2$. Substituting the given values, we get $(x - 1)^2 + (y - 2)^2 = 3^2$, or $(x - 1)^2 + (y - 2)^2 = 9$.