Update cheatsheet.fr.md

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

@@ -807,8 +807,8 @@ Le modèle mathémait
 
 $`\begin{align} \quad &=A\;\big[\,cos(\underbrace{\omega t - kx}_{\color{blue}{\text{  posons }\\ \omega t - kx \,=\, \alpha}} + \varphi_1) + cos(\underbrace{\omega t - kx}_{\color{blue}{=\; \alpha}} + \varphi_1)\,\big]
 &\\
-&=A\;\big[\,cos\Big(\alpha + \dfrac{\varphi_1+\varphi_2}{2} + \dfrac{\varphi_1-\varphi_2}{2}\Big) \\
-&\quad\quad\quad\quad + \,cos\Big(\alpha + \dfrac{\varphi_1+\varphi_2}{2} - \dfrac{\varphi_1-\varphi_2}{2}\Big)\,\Big]\\
+&=A\;\big[\,cos\Big(\alpha + \underbrace{\dfrac{\varphi_1+\varphi_2}{2} + \dfrac{\varphi_1-\varphi_2}{2}}_{\color{blue}{=\;\varphi_1}}\Big) \\
+&\quad\quad\quad\quad + \,cos\Big(\alpha + \underbrace{\dfrac{\varphi_1+\varphi_2}{2} - \dfrac{\varphi_1-\varphi_2}{2}}_{\color{blue}{=\;\varphi_1}}\Big)\,\Big]\\
 &\\
 &=A\;\big[\,cos\Big(\underbrace{\alpha + \dfrac{\varphi_1+\varphi_2}{2}}_{\color{blue}{=\;\alpha '}} + \dfrac{\varphi_1-\varphi_2}{2}\Big) \\
 &\quad\quad\quad\quad + \,cos\Big(\underbrace{\alpha + \dfrac{\varphi_1+\varphi_2}{2}}_{\color{blue}{\text{nous avons posé }\\ \alpha + (\varphi_1+\varphi_2)/2\; = \;\alpha '}} - \dfrac{\varphi_1-\varphi_2}{2}\Big)\,\Big]\\