Any point P with coordinates (\(x, y\)) on the circumference of a circle can be joined to the centre (0, 0) by a straight line that forms the hypotenuse of a right angle triangle with sides of length ...

and \(\sqrt {{g^2} + {f^2} - c}\) is the radius. Notice that for the circle to exist, \({g^2} + {f^2} - c\textgreater0\). Look at the following worked examples.