The equation is .

Test for symmetry with respect to x - axis:

                              (Replace y with y)

This is not 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  an equivalent equation.

Origin is the symmetry.