I don't know what your " a " and " b " stand for, but it looks like you want the equation of a circle with its center at (1, 4) that passes through (1, 13) .
the radius of the circle = the distance between the center and a point on the circle
the radius of the circle = the distance between (1, 4) and (1, 13)
Notice how the (1, 4) and (1, 13) both have the same x coordinate.
So the distance between the two points is just 13 - 4 .
the radius of the circle = 13 - 4 = 9
So we know that r = 9 , h = 1 , and k = 4 .
Plugging these values directly into the standard form of a circle.....
(x - h)2 + (y - k)2 = r2
(x - 1)2 + (y - 4)2 = 92
(x - 1)2 + (y - 4)2 = 81 This is the equation of the circle, and here's a graph of it.