Update cheatsheet.fr.md

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

@@ -105,9 +105,9 @@ $`\quad = \left(
 $`\overrightarrow{grad}\big(div\,\overrightarrow{U}\big)`$
 $`\quad = \left(
 \begin{array}{l}
-\dfrac{\partial^2 U_x}{\partial x^2}+\partial^2 U_y}{\partial x \partial y}+\partial^2 U_z}{\partial x \partial z}\\
-\dfrac{\partial^2 U_x}{\partial y \partial x}+\partial^2 U_y}{\partial y^2}+\partial^2 U_z}{\partial y \partial z}\\
-\dfrac{\partial^2 U_x}{\partial z \partial x}+\partial^2 U_y}{\partial z \partial y}+\partial^2 U_z}{\partial z^2}
+\dfrac{\partial^2 U_x}{\partial x^2}+\dfrac{\partial^2 U_y}{\partial x \partial y}+\dfrac{\partial^2 U_z}{\partial x \partial z}\\
+\dfrac{\partial^2 U_x}{\partial y \partial x}+\dfrac{\partial^2 U_y}{\partial y^2}+\dfrac{\partial^2 U_z}{\partial y \partial z}\\
+\dfrac{\partial^2 U_x}{\partial z \partial x}+\dfrac{\partial^2 U_y}{\partial z \partial y}+\dfrac{\partial^2 U_z}{\partial z^2}
 \end{array}\right)`$