%% 
%%  Ein Beispiel der DANTE-Edition
%%  
%%  2. Auflage
%% 
%%  Beispiel 17-03-2 auf Seite 844.
%% 
%%  Copyright (C) 2016 Herbert Voss
%% 
%%  It may be distributed and/or modified under the conditions
%%  of the LaTeX Project Public License, either version 1.3
%%  of this license or (at your option) any later version.
%% 
%%  See http://www.latex-project.org/lppl.txt for details.
%% 
%% 
%% ==== 
% Show page(s) 1
%% 
%% 
\documentclass[]{exaarticle}
\pagestyle{empty}
\setlength\textwidth{352.81416pt}
\setlength\parindent{0pt}
\usepackage[utf8]{inputenc}
%StartShownPreambleCommands
\usepackage{expl3}              % expl3 lädt auch l3fp
\ExplSyntaxOn \cs_new_eq:NN \calculate \fp_eval:n \ExplSyntaxOff
%StopShownPreambleCommands
\begin{document}
Der Pythagoras in Winkelform:
$\sin^2 45+\cos^2 45=\calculate{(sin(45)^2)+(cos(45))^2}$, was ungefähr
gleich $\calculate{round((sin(45)^2)+(cos(45))^2,2)}$ ist.
\end{document}