diff --git a/00.brainstorming-pedagogical-teams/40.collection-existing-pedagogical-content/04.reference-frames-coordinate-systems/textbook.fr.md b/00.brainstorming-pedagogical-teams/40.collection-existing-pedagogical-content/04.reference-frames-coordinate-systems/textbook.fr.md
index df2c897d9..a4e63b480 100644
--- a/00.brainstorming-pedagogical-teams/40.collection-existing-pedagogical-content/04.reference-frames-coordinate-systems/textbook.fr.md
+++ b/00.brainstorming-pedagogical-teams/40.collection-existing-pedagogical-content/04.reference-frames-coordinate-systems/textbook.fr.md
@@ -435,7 +435,7 @@ de déplacement du point $`M`$ lorsque seule la coordonnée $`\rho`$ croît de f
 of the point $`M`$ when only the coordinate $`\rho`$ increases in an infinitesimal way) writes :<br>
 <br>$`\overrightarrow{e_{\rho}}=\dfrac{\partial\overrightarrow{OM}_{\rho}}{||\partial\overrightarrow{OM}_{\rho}||}`$<br>
 <br>tambien / de même / similarly :<br>
-$`\partial\overrightarrow{OM}_{\varphi}}=\dfrac{\partial \overrightarrow{OM}}{\partial \varphi}\cdot d\varphi`$,
+$`\partial\overrightarrow{OM}_{\varphi}=\dfrac{\partial \overrightarrow{OM}}{\partial \varphi}\cdot d\varphi`$,
 $`\quad\overrightarrow{e_{\varphi}}=\dfrac{\partial\overrightarrow{OM}_{\varphi}}{||\partial\overrightarrow{OM}_{\varphi}||}`$<br>
 $`\partial\overrightarrow{OM}_z=\dfrac{\partial \overrightarrow{OM}}{\partial z}\cdot dz`$,
 $`\quad\overrightarrow{e_z}=\dfrac{\partial\overrightarrow{OM}_z}{||\partial\overrightarrow{OM}_z||}`$