The equation is .

Test for symmetry with respect to x - axis:

                        (Replace y with y)

This is an equivalent equation.

Test for symmetry with respect to y - axis:  

                        (Replace x with x)

This is not an equivalent equation.

Test for symmetry with respect to origin:

                  (Replace y with y and x with x)

This is not an equivalent equation.

x - axis is the symmetry.