Update cheatsheet.fr.md

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

@@ -1502,7 +1502,7 @@ $`\quad\quad \;\; = \cdots`$
     &\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>
-   **$`\begin{array}\quad = \underbrace{2\,A\,\,cos\big(\Delta \omega_{1-2} t \varphi_B)}_{\color{blue}{\text{lentement variable\\fonction enveloppe}}} \times cos\,(\omega_{moy} t + \varphi_A)
+   **$`\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}`$**