Update cheatsheet.fr.md

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

@@ -877,9 +877,13 @@ $`\quad\boldsymbol{\mathbf{=\color{brown}{2\,A\cdot cos\Big(\dfrac{\varphi_1-\va
    $`\color{blue}{\scriptsize{\quad\text{et regroupons encore les termes communs.}}}`$   
    <br>
    $`\quad = A\;e^{\,i\,(\omega t\,-\, kx)}\,e^{\,i\,\left(\frac{\varphi1 + \varphi2}{2}\right)}`$
-   $`\cdot\left(\,e^{\,i\left(\frac{\varphi1-\varphi2}{2}\right)}\,+\,e^{\,-\,i\;\left(\frac{\varphi1-\varphi2}{2}\right)}\right)`$
+   $`\cdot\left(
+\,e^{\,i\Big(\frac{\varphi1-\varphi2}{2}\Big)}
+\,+\,
+e^{\,-\,i\;\Big(\frac{\varphi1-\varphi2}{2}\Big)}
+\right)`$
    <br>
-   $`\color{blue}{\scriptsize{\quad \text{utilisons } exp\,(i\,a)\,+\,exp\,(-\,i\,a)\;=\;2\,cos\,a}}`$  
+   $`\color{blue}{\scriptsize{\quad \text{utilisons} \quad exp\,(i\,a)\,+\,exp\,(-\,i\,a)\;=\;2\,cos\,a}}`$  
    <br>
    $`\quad = A\;e^{\,i\;(\omega t\,-\, kx)}\,e^{\,i\left(\frac{\varphi1 + \varphi2}{2}\right)}`$
    $`\cdot cos\left(\frac{\varphi1-\varphi2}{2}\right)`$