Zeile 61:
Zeile 61:
<math>
<math>
\begin{eqnarray}
\begin{eqnarray}
−
A &= &2\pi r^2 + \frac{2000}{r}
+
A &= &2\pi r^2 + \frac{2000}{r}\\
−
A' &= &4\pi r - \frac{2000}{r^2}
+
A' &= &4\pi r - \frac{2000}{r^2}\\
−
0& =& 4\pi r - \frac{2000}{r^2}
+
0& =& 4\pi r - \frac{2000}{r^2}\\
&\rightarrow& r ≈ 5,419cm
&\rightarrow& r ≈ 5,419cm
\end{eqnarray}</math>
\end{eqnarray}</math>