The standard equation of a circle is



Substituting the three points we have this system:



Simplifying and rearranging the terms:



Subtracting the third equation from the first:





Subtracting the second equation from the first:




Substituting 2k for h






So the center = (h,k) = (2,1)

Substituting h=2 and k=1 in the first equation








The equation

 becomes



Or if you multiply that out and get the general form:




Edwin