Question

What is the equation of this circle?

Answer 1

x2 + (y + 1)2 = 4

x2 + (y – 1)2 = 2

x2 + (y + 1)2 = 2

x2 + (y – 1)2 = 4

Answer 2

First notice that the radius is 2, and the center is at the point (0,1).

Also know that the equation for a circle is:\[(x-a)^2+(y-b)^2=r^2\]

r=radius
a= x-coordinate of the center
b= y-coordinate of the center,

So what should the equation be?