Update cheatsheet.fr.md

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

@@ -1494,15 +1494,15 @@ $`\quad\quad \;\; = \cdots`$
 
 * L'équation de ce phénomène se résume à :   
    <br>
-  **$`U(\overrightarrow{r},t)`$**  
+  **$`\mathbf{\boldsymbol{U(\overrightarrow{r},t)}}`$**  
   $`\begin{array}\quad = &+\,2\,\color{blue}{\underbrace{A_{moy}}_{=\;A}}\,cos\big(\omega_{moy} t + \color{blue}{\underbrace{\overrightarrow{k}_{moy}\cdot\overrightarrow{r}+ \varphi_{moy}}_{=\;\varphi_A}} \big)\\
     &\quad\times\,cos\big(\Delta \omega_{1-2} t + \color{blue}{\underbrace{\Delta \overrightarrow{k}_{1-2}\cdot\overrightarrow{r}+\Delta\varphi_{1-2}}_{=\;\varphi_B}}\big)\\
    &-\,2\,\color{blue}{\underbrace{\Delta A_{1-2}}_{=\;0}}\,sin\big(\omega_{moy} t + \overrightarrow{k}_{moy}\cdot\overrightarrow{r}+ \varphi_{moy}\big)\\
     &\quad\times\,sin\big(\Delta \omega_{1-2} t + \Delta \overrightarrow{k}_{1-2}\cdot\overrightarrow{r}+\Delta\varphi_{1-2}\big)
     \end{array}`$    
    <br>
-   $`\begin{array}\quad = \underbrace{2\,A\,\,cos\big(\Delta \omega_{1-2} t \varphi_B)_{\color{blue}{\text{lentement variable\\fonction enveloppe}}} \times cos\,(\omega_{moy} t + \varphi_A)`$
-   \end{array}`$ 
+   **$`\begin{array}\quad = \underbrace{2\,A\,\,cos\big(\Delta \omega_{1-2} t \varphi_B)}_{\color{blue}{\text{lentement variable\\fonction enveloppe}}} \times cos\,(\omega_{moy} t + \varphi_A)`$
+   \end{array}`$** 
 
 
 *  Écoutons ce phénomène :