Curves may also be given in polar form as in the three leaved rose . However, this command is in the plots package. Examine what happens if you increase or decrease the ranges for x and y - try several changes. For implicitplot , it is advisable to start with a large range and then decrease the range until the graph is satisfactory.
Some remarks are in order here.
Curves which can be plotted using plot may also be plotted using implicitplot but not vice versa. Wherever possible use plot instead of implicitplot because plot is faster and gives more accurate graphs.