Update cheatsheet.fr.md

12.temporary_ins/69.waves/30.n3/20.overview/cheatsheet.fr.md

@@ -1716,8 +1716,10 @@ $`\quad\quad \;\; = \cdots`$
    &+\,2i\,\Delta A_{1-2}\,sin\,\theta_{12}\;(cos\,\theta_{moy}\,+\,i\,sin\,\theta_{moy})\big]\end{align}`$  
   <br>
   $`\; \begin{align}= & \,2\,\times\\
-  &\mathscr{R}e \big[(\,A_{moy}\,cos\,\theta_{12}\;cos\,\theta_{moy}\,-\,\Delta A_{1-2}\,sin\,\theta_{12}\;sin\,\theta_{moy}\,) \\
-  &\,+\,i\,(\,A_{moy}\,cos\,\theta_{12}\;sin\,\theta_{moy}\,+\,\Delta A_{1-2}\,sin\,\theta_{12}\;cos\,\theta_{moy}\,)\big] \\
+  &\mathscr{R}e \big[(\,A_{moy}\,cos\,\theta_{12}\;cos\,\theta_{moy}\\
+  &\quad\quad\quad -\,\Delta A_{1-2}\,sin\,\theta_{12}\;sin\,\theta_{moy}\,) \\
+  &\,+\,i\,(\,A_{moy}\,cos\,\theta_{12}\;sin\,\theta_{moy}\\
+  &\quad\quad\quad +\,\Delta A_{1-2}\,sin\,\theta_{12}\;cos\,\theta_{moy}\,)\big] \\
   \end{align}`$    
 
   **$`\mathbf{\boldsymbol{\begin{array}\quad = &+\,2\,A_{moy}\,cos\big(\omega_{moy} t + \overrightarrow{k}_{moy}\cdot\overrightarrow{r}+ \varphi_{moy}\big)\\