\documentstyle[12pt]{article} 
\pagestyle{empty}
\begin{document}
\large
\begin{eqnarray}
\sf 
\vec{r} & = & \vec{r}_n + c_1 h \vec{p}_n + c_2 h^2 \vec{F}_n \nonumber \\
\vec{p} & = & c_0 \vec{p}_n + (c_1-c_2) h \vec{F}_n \nonumber \\
\vec{F}_{n+1} & = & \vec{F}(\vec{r}) \nonumber \\
\vec{r}_{n+1} & = & \vec{r} + \delta\vec{r} \nonumber \\
\vec{p}_{n+1} & = & c_2 h \vec{F}_{n+1} + \delta\vec{p} \nonumber
\end{eqnarray}
\end{document}
\end{document}
