Find the equation of the circle on the y-axis and has y-intercept at 1 and 7.

Answer 1

the center of the circle is the average of the intercepts ... (1 - 7) / 2 = 4
... center at (0,4)

the radius is the distance from the center to one of the intercepts ... 7 - 4 = 3

the general circle equation is
... (x - h)^2 + (y - k)^2 = r^2
... center at (h,k) , radius = r