Update cheatsheet.fr.md

12.temporary_ins/08.conservative-vector-fields/20.conservative-vector-fields-properties/20.overview/cheatsheet.fr.md

@@ -434,8 +434,13 @@ $`\mathbf{d\phi=\left.\dfrac{\partial \phi}{\partial \alpha}\right|_M\cdot dl_{\
 La comparaison terme à terme de ces deux expressions de $d\phi`$ donne l'expression de 
 $`\overrightarrow{grad}\,\phi`$ en coordonnées $`(d\alpha\,,d\beta\,,d\gamma)`$ :
 
-
-
+$`\left.\begin{align}{l}
+\d\phi=X_{\alpha}\,dl_{\alpha}+X_{\beta}\,dl_{\beta}+X_{\gamma}\,dl_{\gamma}\\
+\d\phi=\dfrac{\partial \phi}{\partial dl_{\alpha}}\,\dfrac{\partial dl_{\alpha}}{\partial \alpha}\,d\alpha
++\dfrac{\partial \phi}{\partial dl_{\beta}}\,\dfrac{\partial dl_{\beta}}{\partial \beta}\,d\beta
++\dfrac{\partial \phi}{\partial dl_{\gamma}}\,\dfrac{\partial dl_{\gamma}}{\partial \gamma}\,d\gamma\\
+\end{align}\right\}`$
+$`\Longrightarrow`$