Update textbook.fr.md

01.curriculum/01.physics-chemistry-biology/04.Niv4/04.electromagnetism/02.electromagnetic-waves-vacuum/02.electromagnetic-waves-vacuum-main/textbook.fr.md

@@ -3,3 +3,6 @@ title : electrostatics-in-matter-main
 published : false
 visible : false
 ---
+$`\overrightarrow{rot}\,\overrightarrow{E}
+=
+-\dfrac{\partial \overrightarrow{B}}{\partial t}`$