\documentclass{article}
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{amsfonts}

\thispagestyle{empty}
\begin{document}

\[
r = \dfrac{l}{2 \sin \dfrac {\pi}{5}} = \dfrac{100 \sqrt{3}\ cr}{2 \sin \dfrac {\pi}{5}} =
\dfrac{173.20508\ cr}{1.17557} = 147.3371\ cr
\]

\end{document}
