'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'

def equation(self, x='x', y='y'):

    x = _symbol(x)
    y = _symbol(y)
    t1 = (((x - self.center.x) / self.hradius) ** 2)
    t2 = (((y - self.center.y) / self.vradius) ** 2)
    return ((t1 + t2) - 1)
