Update cheatsheet.fr.md

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

@@ -1655,11 +1655,7 @@ $`= 2\,A\,\,cos\big(\Delta \omega_{1-2} t + \varphi_B) \times cos\,(\omega_{moy}
 \color{blue}{\text{terme lentement variable de fréquence} \\ \nu\, = \,\left|\frac{\nu_1 - \nu_2}{2}\right| = \left|\frac{440 - 441}{2}\right|=0,5\,Hz\,\lt\,20\,Hz \\ \text{terme de battement}
 }}}`$**   
 **$`\quad\quad\quad\mathbf{
-\times \underbrace{
-cos\,(\omega_{moy} t + \varphi_A)
-}_{
-\color{grey}{\text{terme de fréquence} \\ \nu_{moy}\,=\,440,5\,Hz\,\gt\,20\,Hz}
-}`$**  
+\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)}_{