Update cheatsheet.fr.md

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

@@ -593,9 +593,9 @@ $`\quad\boldsymbol{\mathbf{=\color{brown}{2\,A\cdot cos\Big(\dfrac{\varphi_1-\va
   
 * Calcul de l'onde complexe résultante :  
   <br>
-  $`\color{brown}{\mathbf{\underline{U}(x,t)}}\; = \underline{U_1}(x,t) + \underline{U_2}(x,t)`$ 
+  $`\mathbf{\underline{U}(x,t)}`$$`\; = \underline{U_1}(x,t) + \underline{U_2}(x,t)`$ 
   <br>
-  $`\quad &=A\;\big[\,e^{\,i\;(kx - \omega t+ \varphi_1)} + e^{\,i\;(kx - \omega t+ \varphi_2)}\,\big]`$  
+  $`\quad =A\;\big[ \,e^{\,i\;(kx - \omega t+ \varphi_1)} + e^{\,i\;(kx - \omega t+ \varphi_2)}\,\big]`$  
   <br>
   $`\color{blue}{\scriptsize{\text{Pour simplifier, poson }kx - \omega t \,=\, \alpha}}`$   
   <br>