Astroid Radial Curve

$\begin{figure}\begin{center}\BoxedEPSF{AstroidRadial.epsf scaled 500}\end{center}\end{figure}$

$\displaystyle x$	$\textstyle =$	$\displaystyle x_0 + 3 a\cos t - 3 a\cos(3 t)$
$\displaystyle y$	$\textstyle =$	$\displaystyle y_0 + 3 a\sin t + 3 a\sin(3 t).$