diff --git a/01.curriculum/01.physics-chemistry-biology/04.Niv4/04.electromagnetism/02.electromagnetic-waves-vacuum/02.electromagnetic-waves-vacuum-main/textbook.fr.md b/01.curriculum/01.physics-chemistry-biology/04.Niv4/04.electromagnetism/02.electromagnetic-waves-vacuum/02.electromagnetic-waves-vacuum-main/textbook.fr.md
index 8f47f260c..71016174e 100644
--- a/01.curriculum/01.physics-chemistry-biology/04.Niv4/04.electromagnetism/02.electromagnetic-waves-vacuum/02.electromagnetic-waves-vacuum-main/textbook.fr.md
+++ b/01.curriculum/01.physics-chemistry-biology/04.Niv4/04.electromagnetism/02.electromagnetic-waves-vacuum/02.electromagnetic-waves-vacuum-main/textbook.fr.md
@@ -63,4 +63,12 @@ $`\overrightarrow{rot} \, \left( \overrightarrow{rot}\,\overrightarrow{E} \right
 
 La reconstruction de 
 $`\Delta \;\overrightarrow{E} =\overrightarrow{grad} \left(div\;\overrightarrow{E}\right) - \overrightarrow{rot}\, \left(\overrightarrow{rot}\;\overrightarrow{E}\right)`$
-a +, je dois y aller
+donne :
+
+$`\Delta \;\overrightarrow{E} = \overrightarrow{grad}\left( \dfrac{\rho}{\epsilon_O} \right) + \mu_0\;\dfrac{\partial \overrightarrow{j}}{\partial t}  +
+\mu_0 \epsilon_0 \;\dfrac{\partial^2 \overrightarrow{E}}{\partial t^2}`$
+
+ce qui donne par identification au premier terme de l'équation d'onde :
+
+$`\Delta \;\overrightarrow{E}-\mu_0 \epsilon_0 \;\dfrac{\partial^2 \overrightarrow{E}}{\partial t^2} = \overrightarrow{grad}\left( \dfrac{\rho}{\epsilon_O} \right) + \mu_0\;\dfrac{\partial \overrightarrow{j}}{\partial t}  +
+\mu_0 \epsilon_0 \;\dfrac{\partial^2 \overrightarrow{E}}{\partial t^2}`$