Let the center coordinate be (x, y) and the center of the last circle be (0,2). Because the two circles are circumscribed and tangent to the axis, the distance between the centers of the two circles is equal to the sum of the radii of the two circles. The radius of circle two should be y.

So the square of (y-2)+the square of x = the square of (y+2) gives 3y = (the square of x).