Update cheatsheet.fr.md

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

@@ -352,7 +352,7 @@ $`\forall \alpha \in \mathbb{R}\;,\,`$ **$`\large{exp{\,\alpha} = cos \,\alpha +
                &\quad\quad\text{avec }\mathbf{\color{blue}{\underline{A}=A\; e^{\,i\varphi} }}\\
                &\quad\quad\quad\color{blue}{\text{amplitude complexe}}\end{align}`$
 
-     3D : **$`\quad{\boldsymbol{\mathbf{\large{\underline{U}(\vec{r},t) &=A\cdot e^{\,i\,(\omega t - \vec{k}\cdot\vec{r} + \varphi)}}}}`$**    
+     3D : **$`\quad\boldsymbol{\mathbf{\large{\underline{U}(\vec{r},t) &=A\cdot e^{\,i\,(\omega t - \vec{k}\cdot\vec{r} + \varphi)}}}`$**    
             $`\quad\quad\quad\ =A\cdot e^{\,i\,(\omega t - \vec{k}\cdot\vec{r})}\cdot  e^{\,i\varphi}`$     
             $`\quad\quad\quad\ =A\cdot  e^{\,i\varphi)}\cdot e^{\,i\,(\omega t - \vec{k}\cdot\vec{r})}`$   
           **$`\quad\quad\quad\ =\mathbf{\underline{A}\cdot e^{\,i\,(\omega t - \vec{k}\cdot\vec{r})}}`$**