Update cheatsheet.fr.md

12.temporary_ins/90.electromagnetism-in-vacuum/30.maxwell-electromagnetism-potentials/cheatsheet.fr.md

@@ -140,8 +140,9 @@ $`\color{blue}{\scriptsize{\left.\begin{align} &\forall \phi\,,\,
   &\overrightarrow{rot}\,\overrightarrow{U}=0\end{align}\right\}\Longrightarrow
   \exists\phi'\,,\, \overrightarrow{U}=-\,\overrightarrow{grad}\,\phi'}}`$   
 <br>
-$`\exists V\,,\, \overrightarrow{E}+\dfrac{\partial \overrightarrow{A}}{\partial t}=-\,\overrightarrow{grad}\,V`$
-
+$`\exists V\,,\, \overrightarrow{E}+\dfrac{\partial \overrightarrow{A}}{\partial t}=-\,\overrightarrow{grad}\,V`$   
+<br>
+**$`\large{\mathbf{\overrightarrow{E}=-\,\overrightarrow{grad}\,V-\dfrac{\partial \overrightarrow{A}}{\partial t}}}`$**
 
 
 $`\Longrightarrow \overrightarrow{rot}\,\left(\overrightarrow{E}+\dfrac{\partial \overrightarrow{A}