-\documentclass[a4paper,10pt]{article}
+\documentclass[a4paper,10pt,fleqn]{article}
\usepackage[utf8x]{inputenc}
\usepackage{amsmath,amssymb}
\usepackage{fullpage}
+
+\def\Z{\mathbb{Z}}
+\def\kgV{\text{kgV}}
+\def\ggT{\text{ggT}}
+\def\sgn{\text{sgn}}
%opening
\title{}
\author{Peter Schaefer}
\begin{document}
\maketitle
\section*{1.Übung}
-\subsection*{2. Aufgabe}
+\subsection*{1. Aufgabe}
+\begin{align}
+ S_n &= \frac 1 1 + \frac 1 2 + \cdots + \frac 1 n \in \Z\\
+ n &= 1 ;\\ & \Rightarrow S_1 \in \Z\\
+n & \geq 2 :\\
+a & = \kgV(1,2,\dots,n)\\
+S_n &= \frac{\frac a 1 + \frac a 2+ \cdots \frac a n} a\\ &=
+\frac{ \overbrace{\frac a 1 + \frac a 2 + \cdots}^{\text{gerade}} + \overbrace{\frac a {2^k}}^{\text{ungerade}} + \overbrace{\cdots + \frac a n}^{\text{gerade}}} {\underbrace{a}_{\text{gerade}}} = \frac{\text{ungerade}}{\text{gerade}} \Rightarrow S_n \notin \Z,n \in \{2,3,\dots\}
+\end{align}
-\begin{eqnarray*}
-&&\begin{array}{ccccccc}
+\subsection*{3. Aufgabe}
+\begin{align}
+&\begin{array}{ccccccc}
r_{i-2} & r_{i-1}& q_i & x_{i-2} & x_{i-1} & y_{i-2} & y_{i-1}\\
312 & 269 & 1 & 1 & 0 & 0 & 1\\
269 & 43 & 6 & 0 & 1 & 1 & -1\\
11 & 10 & 1 & -6 & 19 & 7 & - 22\\
10 & 1 & & 19 & -25 & -22 & 29\\
\end{array}\\
-\text{ggT}(312,269) & = & 1\\
-1 & = & -25*312+29*269\\
-5 & = & -125*312+145*269\\
-x & = & 5\cdot\binom{-25}{29}+\cdot
-\end{eqnarray*}
+\ggT(312,269) & = & 1\\
+1 & = -25*312+29*269\\
+5 & = -125*312+145*269\\
+x & = 5\cdot\binom{-25}{29}+\cdot
+\end{align}
+
+\subsection*{4. Aufgabe}
+\begin{align}
+ v &= \kgV(a,b) = \frac{|ab|}{\ggT(a,b)}\\
+ &= a\cdot \frac{\sgn(a) |b|}{\ggT(a,b)} = b\cdot \frac{\sgn(b) |a|}{\ggT(a,b)}\\
+&a|w \wedge b|w \Rightarrow ab|bw \wedge ab|aw \Rightarrow ab|\ggT(aw,bw)\Rightarrow|w|\ggT(a,b) \Rightarrow \frac{ab}{\ggT(a,b)}\Big||w|
+\end{align}
+
\end{document}