The equation of
have the four common points , (0,-3),(0,3),(-3,0),(3,0).
These points are intersections with x-axis or y-axis.
So substance x=0 or y=0 for this equation.
Substance x=0
Substance y=0
Therefore ,when n is any number ,the equation have the four common points
of (0,-3),(0,3),(-3,0),(3,0).