On 2010-11-27, Karl Townsend wrote:
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Bonus Algebra question:
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Second note. I said algebra, not trig for a reason. I can draw a
pciture and solve the problem for a given set of data. What I need is
the general case, given four X values and four Y values: what formula
can I enter into the computer to give the answer? At least for me,
this is MUCH harder to do.

All you need to know

http://en.wikipedia.org/wiki/Circumscribed_circle