Question 1060075
I made an Excel sheet that does that.
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|x  y  x^2+y^2 1|
|x1 y1 x1+y1^2 1|
|x2 y2 x2+y2^2 1| = 0
|x3 y3 x3+y3^2 1|

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Without the sheet, I would do it like this:
A(-5,-1)
B(-11,-9)
C(-4,-8)
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Find the perpendicular bisector of AB, and of BC
Find the intersection of the 2 bisectors, that's the center.
The radius is the distance from the center to any point.