Latex Mathematics

I found out how to handle simple Mathematic structures:
Here is the tex-code:

\documentclass[fontsize=11pt]{scrartcl}
\usepackage{ucs}
\usepackage[utf8x]{inputenc}
\usepackage[T1]{fontenc}
\usepackage[ngerman]{babel}
\PrerenderUnicode{ä,ö,ü,Ä,Ö,Ü,ß}

%nur für Mathe
\usepackage{amsmath,amssymb,amstext}
\usepackage{oldgerm}

%Für eigene Kopf und Fußzeilen
\usepackage[automark]{scrpage2}
\pagestyle{scrheadings}
\clearscrheadfoot
\ifoot[]{Christian Jähnl}
\chead[]{Mathematik}
\ofoot[]{\pagemark}

%Trennungsline unter Kopfzeile
\setheadsepline[\textwidth]{1pt}

\begin{document}

\section*{Matritzen}
\label{sec:matritzen}

\begin{center}<

\begin{equation}
\begin{Vmatrix}

a_{11} & a_{12} & a_{13} \\
a_{21} & a_{22} & a_{23} \\
a_{31} & a_{32} & a_{33}

\end{Vmatrix}
= \textfrak{A}
\end{equation}
Allgemeine Matrix

\begin{equation}
\begin{vmatrix}
1 & 0 & 0 \\
0 & 1 & 0 \\
0 & 0 & 1
\end{vmatrix}
=\textfrak{E}
\end{equation}
Einheitsmatrix

\end{center}

\section*{Rahmen}
\label{sec:rahmen}

\begin{equation}
\boxed{
\begin{gathered}
a^2+b^2=c^2 \\
\sigma + \alpha = \beta
\end{gathered}
}
\end{equation}

\section*{Wurzel}
\label{sec:wurzel}

\begin{equation}
r= \sqrt[3]{\frac{3V}{4\pi}}
\end{equation}

\end{document}

And this is what you get: Mathematik