Update cheatsheet.fr.md

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

@@ -32,12 +32,12 @@ div\,\overrightarrow{X}}\color{black}{\;=\dfrac{d\Phi_X}{d\tau}}\, = &\dfrac{1}{
 & \quad\quad\quad\quad + \dfrac{1}{r\,sin\,\theta}\;\dfrac{\partial\,X_{\varphi}}{\partial\,\varphi}
 \end{align}}}`$**
 
-**$`\mathbf{\begin{align}
+**$`\boldsymbol{\mathbf{\begin{align}
 div\,\overrightarrow{X} = \color{black}{\;=\dfrac{d\Phi_X}{d\tau}}\,= &\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}}`$**
+& \quad\quad\quad\quad + \dfrac{1}{r\,sin\,\theta}\;\dfrac{\partial\,X_{\varphi}}{\partial\,\varphi}\end{align}}}`$**
 
 **$`\color{black}{\;=\dfrac{d\Phi_X}{d\tau}}`$**