Update cheatsheet.fr.md

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

@@ -60,9 +60,9 @@ $`\newcommand{\ddpt}[1]{\overset{\large\bullet\bullet}{#1}}`$
 
 
 
-$`\begin{align} \mathbf{\color{brown}{U(&x,t)}} = U_1(x,t) + U_2(x,t) \\
-&\\
-&=A\;\big[\,cos(\underbrace{kx - \omega t}_{\text{  posons }\\ kx - \omega t \,=\, \alpha} + \varphi_1) + cos(\underbrace{kx - \omega t}_{=\; \alpha} + \varphi_1)\,\big]
+**$`\mathbf{U(&x,t)}`$**$`\; = U_1(x,t) + U_2(x,t)
+<br>
+$`\begin{align} \quad &=A\;\big[\,cos(\underbrace{kx - \omega t}_{\text{  posons }\\ kx - \omega t \,=\, \alpha} + \varphi_1) + cos(\underbrace{kx - \omega t}_{=\; \alpha} + \varphi_1)\,\big]
 &\\
 &=A\;\big[\,cos\Big(\alpha + \dfrac{\varphi_1+\varphi_1}{2} + \dfrac{\varphi_2-\varphi_2}{2}\Big) \\
 &\quad\quad\quad\quad + \,cos\Big(\alpha + \dfrac{\varphi_2+\varphi_2}{2} + \dfrac{\varphi_1-\varphi_1}{2}\Big)\,\Big]\\