def equation(self, x='x', y='y'):
        """The equation of the circle.

        Parameters
        ==========

        x : str or Symbol, optional
            Default value is 'x'.
        y : str or Symbol, optional
            Default value is 'y'.

        Returns
        =======

        equation : SymPy expression

        Examples
        ========

        >>> from sympy import Point, Circle
        >>> c1 = Circle(Point(0, 0), 5)
        >>> c1.equation()
        x**2 + y**2 - 25

        """
        x = _symbol(x)
        y = _symbol(y)
        t1 = (x - self.center.x)**2
        t2 = (y - self.center.y)**2
        return t1 + t2 - self.major**2
dataset/ETHPy150Open sympy/sympy/sympy/geometry/ellipse.py/Circle.equation/original