Update cheatsheet.fr.md

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

@@ -610,9 +610,16 @@ $`\quad\boldsymbol{\mathbf{=\color{brown}{2\,A\cdot cos\Big(\dfrac{\varphi_1-\va
   <br>
   $`\color{blue}{\scriptsize{\quad\text{Rappel : }e^{\,i\,a} = cos (a) + i\,sin (a)}}`$   
   $`\color{blue}{\scriptsize{\quad\text{et pour simplifier l'écriture, posons :}}}`$   
-  $`\color{blue}{\scriptsize{\quad\ cos (a) = c\,a \text{  et  } i\,sin (a)}}`$
+  $`\color{blue}{\scriptsize{\quad\ cos (a) = "c\,a" \text{ , et  } sin (a) = "s\,a"}}`$   
   <br>
+  $`\quad =A\;\[ (c\,\alpha\;+\;i\,s\,\alpha) \cdot (c\,\varphi_1\;+\;i\,s\,\varphi_1\;+\;c\,\varphi_2\;+\;i\,s\,\varphi_2)\,]`$  
+  <br>
+  $`\quad =A\;\big[ (c\,\alpha\;+\;i\,s\,\alpha) \cdot \big(\,(c\,\varphi_1\;+\;c\,\varphi_2)\;+\; i\,(s\,\varphi_1\;+\;s\,\varphi_2)\,\big)\big]`$   
+  <br>
+  $`\quad =A\;\big[ (c\,\alpha\;+\;i\,s\,\alpha) \cdot \big(\,(c\,\varphi_1\;+\;c\,\varphi_2)\;+\; i\,(s\,\varphi_1\;+\;s\,\varphi_2)\,\big)\big]`$
+
 
+i\,s\,\varphi_1\;+\;c\,\varphi_2\;+\;i\,s\,\varphi_2)\,]`$