Deltoid Radial Curve

$\begin{figure}\begin{center}\BoxedEPSF{DeltoidRadial.epsf scaled 700}\end{center}\end{figure}$

$\displaystyle x$	$\textstyle =$	$\displaystyle x_0 + 4 a\cos\phi - 4 a \cos(2\phi)$
$\displaystyle y$	$\textstyle =$	$\displaystyle y_0 + 4 a\sin\phi + 4 a \sin(2\phi).$