Update cheatsheet.fr.md

12.temporary_ins/08.grad-div-rot/20.div/20.overview/cheatsheet.fr.md

@@ -33,5 +33,12 @@ div\,\overrightarrow{X}\color{black}{\;=\dfrac{d\Phi_X}{d\tau}}\,= &\dfrac{1}{r^
 \\
 & \quad\quad\quad\quad + \dfrac{1}{r\,sin\,\theta}\;\dfrac{\partial\,X_{\varphi}}{\partial\,\varphi}\end{align}}}`$**
 
-**$`\color{black}{\;=\dfrac{d\Phi_X}{d\tau}}`$**
+<br>
+
+**$`\begin{align}
+\mathbf{div\,\overrightarrow{X}}\mathbf{\color{black}{\;=\dfrac{d\Phi_X}{d\tau}}\mathbf{\,= &\dfrac{1}{r^2}\;\dfrac{\partial\,(r^2\,X_r}{\partial\,r}\\
+\\
+& \quad\quad + \dfrac{1}{r\,sin\,\theta}\;\dfrac{\partial\,(sin\,\theta\,X_{\theta})}{\partial\,\theta}\\
+\\
+& \quad\quad\quad\quad + \dfrac{1}{r\,sin\,\theta}\;\dfrac{\partial\,X_{\varphi}}{\partial\,\varphi}\end{align}}}`$**