Update cheatsheet.fr.md

12.temporary_ins/90.electromagnetism-in-vacuum/10.maxwell-equations/20.overview/cheatsheet.fr.md

@@ -728,7 +728,7 @@ $`\mathbf{div\,\big(\overrightarrow{U}\land\overrightarrow{V}\big)=
   div\,\left(\dfrac{\overrightarrow{E}\land\overrightarrow{B}}{\mu_0}\right)
   = -\,\vec{j}\cdot\overrightarrow{E}
   \,-\,\dfrac{\partial}{\partial t}\,\left(
-  \dfrac{\epsilon_0\,E^2}{2}\,-\,\dfrac{B^2}{2\,\mu_0}
+  \dfrac{\epsilon_0\,E^2}{2}\,+\,\dfrac{B^2}{2\,\mu_0}
   \right)
   }`$**