Update cheatsheet.fr.md

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

@@ -640,9 +640,9 @@ $`\quad\boldsymbol{\mathbf{=\color{brown}{2\,A\cdot cos\Big(\dfrac{\varphi_1-\va
      &\times \Big[ \,c\alpha\,c\Big(\dfrac{\varphi_1+\varphi_2}{2}\Big)-s\alpha\,s\Big(\dfrac{\varphi_1+\varphi_2}{2}\Big)\,\Big]
      \end{align}`$
   <br>
-  $`\quad =2\,A\;&c\Big(\dfrac{\varphi_1-\varphi_2}{2}\Big)\,&c\Big(\alpha + \dfrac{\varphi_1-\varphi_2}{2}\Big)`$
+  $`\quad =2\,A\;c\Big(\dfrac{\varphi_1-\varphi_2}{2}\Big)\,c\Big(\alpha + \dfrac{\varphi_1-\varphi_2}{2}\Big)`$
   <br>
-  **$`\boldsymbol{\mathbf{\quad =2\,A\;&cos\Big(\dfrac{\varphi_1-\varphi_2}{2}\Big)\,&cos\Big(kx - \omega t + \dfrac{\varphi_1-\varphi_2}{2}\Big)}}`$**
+  **$`\boldsymbol{\mathbf{\quad =2\,A\;cos\Big(\dfrac{\varphi_1-\varphi_2}{2}\Big)\,cos\Big(kx - \omega t + \dfrac{\varphi_1-\varphi_2}{2}\Big)}}`$**