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authorDavid A. Madore <david+git@madore.org>2012-03-08 19:18:06 +0100
committerDavid A. Madore <david+git@madore.org>2012-03-08 19:18:06 +0100
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[radicaux] Expression brute de cos(2π/13).
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@@ -704,6 +704,17 @@ vaut $\sqrt{-11}$. On obtient finalement :
\end{array}
\]
+\subsubsection{$n=13$} \XXX
+
+\[
+\begin{array}{rl}
+\displaystyle\cos\frac{2\pi}{13}
+&\displaystyle= - \frac{1}{12} + \frac{1}{12} \, \sqrt{13} + \frac{1}{24} {\left(-1 + \sqrt{-3}\right)} \, \root3\of{-\frac{65}{2} - \frac{39}{2} \, \sqrt{-3}}
+- \frac{1}{24} \, {\left(1 + \sqrt{-3}\right)} \root3\of{-\frac{65}{2} + \frac{39}{2} \, \sqrt{-3}}\\
+&\displaystyle + \frac{1}{24} {\left(1 + \sqrt{-3}\right)} \, \root6\of{-\frac{4381}{2} - \frac{195}{2} \, \sqrt{-3}} - \frac{1}{24} \, {\left(-1 + \sqrt{-3}\right)} \root6\of{-\frac{4381}{2} + \frac{195}{2} \, \sqrt{-3}}\\
+\end{array}
+\]
+
\ifx\danslelivre\undefined