Question

The center of a circle is at (−3, 1) and its radius is 9. What is the equation of the circle?

A.) (x+3)2+(y−1)2=81
B.) (x−3)2+(y+1)2=18
C.) (x−3)2+(y+1)2=81
D.) (x+3)2+(y−1)2=18

Answer 1

If a circle has center (a,b) and radius r, the equation is

`(x-a)^2+(y-b)^2=r^2`

So, you have

`(x+3)^2+(y-1)^2=81`