diff --git a/00.brainstorming-pedagogical-teams/40.collection-existing-pedagogical-content/05.classical-mechanics/vector-analysis/textbook.fr.md b/00.brainstorming-pedagogical-teams/40.collection-existing-pedagogical-content/05.classical-mechanics/vector-analysis/textbook.fr.md
index cd826be78..3d8ff588a 100644
--- a/00.brainstorming-pedagogical-teams/40.collection-existing-pedagogical-content/05.classical-mechanics/vector-analysis/textbook.fr.md
+++ b/00.brainstorming-pedagogical-teams/40.collection-existing-pedagogical-content/05.classical-mechanics/vector-analysis/textbook.fr.md
@@ -647,7 +647,17 @@ $`=d\left(A(t)\right)\cdot\overrightarrow{e_x}
 +d\left(B(t)\right)\cdot\overrightarrow{e_y}`$
 $`+A(t)\cdot d\overrightarrow{e_x} + B(t)\cdot d\overrightarrow{e_y}`$
 
+Or les vecteurs $`\overrightarrow{e_x}`$ et $`\overrightarrow{e_y})`$ sont fixes, 
+on a donc :
 
+$`d\left(\overrightarrow{OM}\right)(t)=d\left(A(t)\cdot\overrightarrow{e_x}\right)
++d\left(B(t)\cdot\overrightarrow{e_y}\right)`$
+$`=d\left(A(t)\right)\cdot\overrightarrow{e_x}
++d\left(B(t)\right)\cdot\overrightarrow{e_y}`$
+$`=d\left(t^2\right)\cdot\overrightarrow{e_x}
++d\left(4t\right)\cdot\overrightarrow{e_y}`$
+$`2\,t\,dt\cdot\overrightarrow{e_x}
++4\,dt\cdot\overrightarrow{e_y}`$