Good style advice for tables is available in the documentation for the booktabs
package. Here it is strongly recommended not to use vertical rules, nor double horizontal rules. Furthermore to provide bigger row spacing in the table you should adjust \arraystretch
(which is a command containing a factor) rather than adding blank rows.

\documentclass[a4paper]{article}
\usepackage{ngerman}
\usepackage{booktabs}
\begin{document}
\begin{table}[htb]
\begin{center}
\renewcommand*{\arraystretch}{1.5}
\begin{tabular}{ccc}
\toprule
Bereich (I) in Nm&Bereich (II) in Nm&Bereich (III) in Nm \\
\midrule
\( M_{t1} = 0\) & \( M_{t2} = 150\) & \( M_{t3} = 150\) \\
\( M_{by1}(x) = \frac{450}{43} \cdot x + n\)
& \( M_{by2}(x) = -\frac{450}{43} \cdot x + n\)
& \( M_{by3}(x) = 0\) \\
\( M_{bz1}(x) = \frac{65}{43} \cdot x + n\)
& \( M_{bz2}(x) = -\frac{65}{43} \cdot x + n\)
& \( M_{bz3}(x) = 0\) \\
\bottomrule
\end{tabular}
\end{center}
\caption{Momente \textit{abgelesen}}
\end{table}
\end{document}
\documentclass{...}
, the required\usepackage
's,\begin{document}
, and\end{document}
. That may seem tedious to you, but think of the extra work it represents for TeX.SX users willing to give you a hand. Help them help you: remove that one hurdle between you and a solution to your problem. – jub0bs Jun 22 '14 at 12:45