An online calculator and solver to find the center and radius of a circle given its equation in the form
x^{ 2} + y^{ 2} + a x + b y = c
The calculator uses the following idea: completes the squares as follows
x^{ 2} + a x = (x + a/2)^{ 2}  (a/2)^{ 2}
and y^{ 2} + a y = (y + b/2)^{ 2}  (b/2)^{ 2}
Substitute the above into the original equation and write in the standard form of the equation of a circle
(x  h)^{ 2} + (y  k)^{ 2} = r^{ 2}
such that the center has coordinates (a/2 , b/2) and radius r such that r^{ 2} = c + (a/2)^{ 2} + (b/2)^{ 2}
How to use the calculator
1  Enter the coefficients a, b, c and the number of decimal places desired as real number and press "enter". If the given equation is that of a circle, it will give an answer: the x and y coordinates of the center and the radius.
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