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

        Parameters
        ==========

        x : str, optional
            Label for the x-axis. Default value is 'x'.
        y : str, optional
            Label for the y-axis. Default value is 'y'.

        Returns
        =======

        equation : sympy expression

        See Also
        ========

        arbitrary_point : Returns parameterized point on ellipse

        Examples
        ========

        >>> from sympy import Point, Ellipse
        >>> e1 = Ellipse(Point(1, 0), 3, 2)
        >>> e1.equation()
        y**2/4 + (x/3 - 1/3)**2 - 1

        """
        x = _symbol(x)
        y = _symbol(y)
        t1 = ((self.center.x - x) / self.hradius)**2
        t2 = ((y - self.center.y) / self.vradius)**2
        return t1 + t2 - 1
dataset/ETHPy150Open sympy/sympy/sympy/geometry/ellipse.py/Ellipse.equation/swapped operands of `-`