\documentclass{article}
\begin{document}

This is a test1.
\begin{equation}
  E = mc^{2}
\end{equation}
where c is the velocity of light
\begin{equation}
  c = 299{,}792{,}458 \, \mathrm{m/s}
\end{equation}


One more example is
\begin{equation}
  \frac{\pi}{2} =
  \left( \int_{0}^{\infty} \frac{\sin x}{\sqrt{x}} dx \right)^2 =
  \sum_{k=0}^{\infty} \frac{(2k)!}{2^{2k}(k!)^2} \frac{1}{2k+1} =
  \prod_{k=1}^{\infty} \frac{4k^2}{4k^2 - 1}
\end{equation}


\end{document}

-------execution------------------
> latex xxx.tex
> dvipdf xxx.dvi