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\samepage \begin{equation}% latex2html id marker 7
{{\partial ^2 y }\over{\partial t^2}} ~=~
c^2 \: {{\partial ^2 y }\over{\partial x^2}} ~,
\label{wave_equation}
\end{equation}
}

{\newpage
\clearpage
\samepage \begin{equation}{{y(i,n+1)\:+\:y(i,n-1) \: - \: 2 \: y(i,n)} \over {(\Delta t)^2}}
~\approx~ c^2 \: \left [
{{y(i+1,n)\:+\:y(i-1,n) \: - \: 2 \: y(i,n)} \over {(\Delta x)^2}}
\right ] ~.
\label{discrete}
\end{equation}
}

{\newpage
\clearpage
\samepage \begin{equation}y(i,n+1) ~=~ 2 \: [ 1\: - \: r^2] \: y(i,n) - y(i,n-1) + r^2 \:
\left [ y(i+1,n) + y(i-1,n) \right ] ~,
\label{algor_1}
\end{equation}
}

{\newpage
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\samepage \begin{equation}F_{hammer} ~=~ g(x) \: K \: z^p ~,
\label{hammer_force}
\end{equation}
}

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