Cycloid Radial Curve

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

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