Update cheatsheet.fr.md

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

@@ -865,7 +865,10 @@ $`\quad\boldsymbol{\mathbf{=\color{brown}{2\,A\cdot cos\Big(\dfrac{\varphi_1-\va
   <br>
   $`A\;\big[ \,e^{\,i\;(\omega t\,-\, kx)}\,\big(\,e^{\,i\varphi_1}\,+\,e^{\,i\varphi_1}\big)`$   
   <br>
-  $`A\;\big[ \,e^{\,i\;(\omega t\,-\, kx)}\,\big(\,e^{\,i\left(\dfrac{\varphi1 + \varphi2}{2}+\dfrac{\varphi1-\varpji2}{2}\right)}\,+\,e^{\,i\left\left(\dfrac{\varphi1 + \varphi2}{2}-\dfrac{\varphi1-\varpji2}{2}\right)}\big)`$ 
+  $`A\;\big[ \,e^{\,i\;(\omega t\,-\, kx)}
+   \,\big(\,e^{\,i\left(\dfrac{\varphi1 + \varphi2}{2}+\dfrac{\varphi1-\varpji2}{2}\right)}
+   \,+\,
+   e^{\,i\;\left(\dfrac{\varphi1 + \varphi2}{2}-\dfrac{\varphi1-\varphi2}{2}\right)}\big)`$ 
 
   $`\quad =A\;\big[\,e^{\,i\;(\alpha\, +\, \varphi_1)} + e^{\,i\;(\alpha\, + \,\varphi_2)} \,\big]`$
   <br>