Update textbook.fr.md

12.temporary_ins/40.classical-mechanics/30.n3/07.coherence/textbook.fr.md

@@ -558,7 +558,7 @@ $`\begin{align}
 ---------------
 
 $`\begin{align}
-\dfrac{d^2\overrightarrow{e_{\theta}}}{dt^2}&=\dfrac{d}{dt}\left(\underbrace{\dfrac{d\overrightarrow{e_{\rho}}}{dt}}_{=\omega\,\vec{e_{\theta}}\right)\\
+\dfrac{d^2\overrightarrow{e_{\theta}}}{dt^2}&=\dfrac{d}{dt}\left(\underbrace{\dfrac{d\overrightarrow{e_{\rho}}}{dt}}_{=\omega\,\vec{e_{\theta}}}\right)\\
 \\
 &=\dfrac{d}{dt}\left(\omega\,\overrightarrow{e_{\theta}}\right)\\
 \\