% Gravitational acceleration in Germany
$$9,81\,\frac{m}{s^2}$$

% pq formula
$$x_{1,2} = - \frac{p}{2} \pm \sqrt{\left(\frac{p}{2}\right)^2 - q}$$

% Quadratic formula
$$x_{1,2} = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}$$

% Catalan numbers
\begin{equation*}
  C_n = \frac{1}{n+1} {2n \choose n} = \frac{(2n)!}{(n+1)!n!}
\end{equation*}

% Definition of a factorial
$$n! = \prod_{i=1}^{n} i$$

% Set of all odd natural numbers
$$\{ x \mid x \in \mathds{N}, \mathrm{odd}(x) \}$$

% Elimination $\neg\exists x$
$$\neg\exists x . p(x) \Leftrightarrow \forall x . \neg p(x)$$