answer
x^2 + y^2 = 121
set up equation
the equation of a circle is (x - h)^2 + (y - k)^2 = r^2
where h is the center x coordinate and k is the center y coordinate
values
from the origin (0, 0) we know that h = 0 and k = 0
since the circle passes through (0, -11) the distance from the origin is 11
r =11
r^2 = 121
plug in values
now that we have all the values, we plug them into (x - h)^2 + (y - k)^2 = r^2
(x - h)^2 + (y - k)^2 = r^2
(x - 0)^2 + (y - 0)^2 = 121
x^2 + y^2 = 121