Maltese Cross Curve

$\begin{figure}\begin{center}\BoxedEPSF{MalteseCrossFunction.epsf}\end{center}\end{figure}$

The plane curve with Cartesian equation

$\begin{displaymath} xy(x^2-y^2)=x^2+y^2 \end{displaymath}$

and polar equation

$\begin{displaymath} r^2={1\over\cos\theta\sin\theta(\cos^2\theta-\sin^2\theta)}. \end{displaymath}$

References

Cundy, H. and Rollett, A. Mathematical Models, 3rd ed. Stradbroke, England: Tarquin Pub., p. 71, 1989.