Update cheatsheet.fr.md

12.temporary_ins/08.grad-div-rot/70.combinaisons-of-operators/20.overview/cheatsheet.fr.md

@@ -110,7 +110,7 @@ visible: false
     $`\overrightarrow{U}=U_x\,\overrightarrow{e_x}+U_y\,\overrightarrow{e_y}+U_z\,\overrightarrow{e_z}`$
     * et l'équation d'onde se décompose en :   
 
-    $`\quad\left\{\begin{array}{l}
+    $`\left\{\begin{array}{l}
     \;\left(\dfrac{\partial^2 U_x}{\partial x^2}+\dfrac{\partial^2 U_x}{\partial y^2}+\dfrac{\partial^2 U_x}{\partial z^2}\right)-\dfrac{1}{\mathscr{v}^2}\dfrac{\partial^2 U_x}{\partial t^2}=0\\
     \;\left(\dfrac{\partial^2 U_y}{\partial x^2}+\dfrac{\partial^2 U_y}{\partial y^2}+\dfrac{\partial^2 U_y}{\partial z^2}\right)-\dfrac{1}{\mathscr{v}^2}\dfrac{\partial^2 U_y}{\partial t^2}=0\\    
     \;\left(\dfrac{\partial^2 U_z}{\partial x^2}+\dfrac{\partial^2 U_z}{\partial y^2}+\dfrac{\partial^2 U_z}{\partial z^2}\right)-\dfrac{1}{\mathscr{v}^2}\dfrac{\partial^2 U_z}{\partial t^2}=0