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 574fd7a06..745de1e4c 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
@@ -307,7 +307,7 @@ Propriétés de l'onde EM plane progressive monochromatique dans le vide :
 
 $`\hspace{0.6cm}\Longrightarrow (\overrightarrow{k},\overrightarrow{E},\overrightarrow{B})`$ forment un trièdre direct.
 
-$`\hspace{0.6cm}\Longrightarrow ||\overrightarrow{B}=\dfrac{\overrightarrow{E}}{c}`$
+$`\hspace{0.6cm}\Longrightarrow ||\overrightarrow{B}||=\dfrac{k}{\omega}\,||\overrightarrow{E}||=\dfrac{||\overrightarrow{E}||}{c}`$
 
 --------------------------