Update cheatsheet.fr.md

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

@@ -1648,9 +1648,18 @@ $`\quad\quad \;\; = \cdots`$
 **$`\mathbf{U(\overrightarrow{r},t)}`$**   
 $`= 2\,A\,\,cos\big(\Delta \omega_{1-2} t + \varphi_B) \times cos\,(\omega_{moy} t + \varphi_A)`$   
 <br>
-**$`= \mathbf{\underbrace{2 A\,\,cos\left(2\pi\dfrac{\nu_1 - \nu_2}{2} t + \varphi_B\right)}_{
-   \color{blue}{\text{terme lentement variable de fréquence} \\ \nu\, = \,\left|\frac{\nu_1 - \nu_2}{2}\right| = \left|\frac{440 - 441}{2}\right|=0,5\,Hz\,\lt\,20\,Hz \\ \text{terme de battement}}}}`$**   
-**\quad\quad\quad\mathbf{\times \underbrace{cos\,(\omega_{moy} t + \varphi_A)}_{\color{grey}{\text{terme de fréquence} \\ \nu_{moy}\,=\,440,5\,Hz\,\gt\,20\,Hz }}}`$**  
+**$`= \mathbf{
+\underbrace{
+2 A\,\,cos\left(2\pi\dfrac{\nu_1 - \nu_2}{2} t + \varphi_B\right)
+}_{
+\color{blue}{\text{terme lentement variable de fréquence} \\ \nu\, = \,\left|\frac{\nu_1 - \nu_2}{2}\right| = \left|\frac{440 - 441}{2}\right|=0,5\,Hz\,\lt\,20\,Hz \\ \text{terme de battement}
+}}}`$**   
+**\quad\quad\quad\mathbf{
+\times \underbrace{
+cos\,(\omega_{moy} t + \varphi_A)
+}_{
+\color{grey}{\text{terme de fréquence} \\ \nu_{moy}\,=\,440,5\,Hz\,\gt\,20\,Hz}
+}`$**  
 <br>    
 <br>
 **$`= \mathbf{\underbrace{2 A\,\,cos\left(2\pi\dfrac{\nu_1 - \nu_2}{2} t + \varphi_B\right)}_{