Update cheatshhet.fr.md

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

@@ -63,7 +63,7 @@ GRADIENT  D'UN  CHAMP SCALAIRE
    $`\overrightarrow{grad}\,V=\dfrac{\partial V}{\partial \rho}\,\overrightarrow{e_{\rho}}+\dfrac{1}{\rho}\,\dfrac{\partial V}{\partial \varphi}\,\overrightarrow{e_{\varphi}}+\dfrac{\partial V}{\partial z}\,\overrightarrow{e_z}`$
 
    Coordonnées sphériques :   
-   $`\overrightarrow{grad}\,V=\dfrac{\partial V}{\partial \rho}\,\overrightarrow{e_{\rho}}+\dfrac{1}{\rho}\,\dfrac{\partial V}{\partial \theta}\,\overrightarrow{e_{\theta}}+\dfrac{1}{\rho\,sin\,\theta}\,\dfrac{\partial V}{\partial \varphi}\,\overrightarrow{e_{\varphi}}`$
+   $`\overrightarrow{grad}\,V=\dfrac{\partial V}{\partial r}\,\overrightarrow{e_r}+\dfrac{1}{r}\,\dfrac{\partial V}{\partial \theta}\,\overrightarrow{e_{\theta}}+\dfrac{1}{r\,sin\,\theta}\,\dfrac{\partial V}{\partial \varphi}\,\overrightarrow{e_{\varphi}}`$