$\begin{array}{l} \text{Gegeben:}\\\text{Kreiszahl} \qquad \pi \qquad [] \\ \text{Fläche} \qquad A \qquad [m^{2}] \\ \\ \text{Gesucht:} \\\text{Radius} \qquad r \qquad [m] \\ \\ r = \sqrt{\frac{A}{\pi }}\\ \textbf{Gegeben:} \\ \pi=3\frac{16}{113} \qquad A=5\frac{1}{5}m^{2} \qquad \\ \\ \textbf{Rechnung:} \\ r = \sqrt{\frac{A}{\pi }} \\ \pi=3\frac{16}{113}\\ A=5\frac{1}{5}m^{2}\\ r = \sqrt{\frac{5\frac{1}{5}m^{2}}{3\frac{16}{113} }}\\\\r=1,29m \\\\ \small \begin{array}{|l|} \hline A=\\ \hline 5\frac{1}{5} m^2 \\ \hline 520 dm^2 \\ \hline 5,2\cdot 10^{4} cm^2 \\ \hline 5,2\cdot 10^{6} mm^2 \\ \hline 0,052 a \\ \hline 0,00052 ha \\ \hline \end{array} \small \begin{array}{|l|} \hline r=\\ \hline 1,29 m \\ \hline 12,9 dm \\ \hline 129 cm \\ \hline 1,29\cdot 10^{3} mm \\ \hline 1,29\cdot 10^{6} \mu m \\ \hline \end{array} \end{array}$