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\begin{equation}\label{topo_x} 
 h_{X}(x) =   
\left\{ 
\begin{array}{lcl} 
 1,  &&|x| > S_{x} + V_{x} \\ 
 \frac{1}{2} - \frac{1}{2} \cos (\pi \frac{|x| - V_{x}}{S_{x}}), &&V_{x} < |x| < S_{x} + V_{x}  \\ 
  0, &&|x| < V_{x}.   
\end{array} 
\right.           
\end{equation} 

\documentclass{scrartcl}
\usepackage{amsmath}
\begin{document}


\begin{equation}
 h_{X}(x) =  
	\begin{cases}
		 1, &   |x| > S_{x} + V_{x} \\
 		\frac{1}{2} - \frac{1}{2} \cos \left (\pi \frac{|x| - V_{x}}{S_{x}}\right ), &   V_{x} < |x| < S_{x} + V_{x}  \\
		 0, &  |x| < V_{x}.
	\end{cases}
	\label{topo_x} 
\end{equation} 
oder
\begin{equation}
 h_{X}(x) = 
 	\left\{\begin{aligned}
		 & 1, &  & |x| > S_{x} + V_{x} \\
 		& \frac{1}{2} - \frac{1}{2} \cos \left (\pi \frac{|x| - V_{x}}{S_{x}}\right ), & &   V_{x} < |x| < S_{x} + V_{x}  \\
		 & 0, & &  |x| < V_{x}.
	\end{aligned}\right.
	\label{topo2_x} 
\end{equation} 

\end{document}

\begin{equation}\label{\topo_x}
 h_{X}(x) =  
\left\{
\begin{array}{rcl}
\left 1,&  \right |x| > S_{x} + V_{x} \\ 
\left \frac{1}{2} - \frac{1}{2} \cos (\pi \frac{|x| - V_{x}}{S_{x}}),&  \right V_{x} < |x| < S_{x} + V_{x}  \\
 \left 0,&  \right|x| < V_{x}.  
\end{array}
\right.          
\end{equation}