Update textbook.fr.md

00.brainstorming-pedagogical-teams/40.collection-existing-pedagogical-content/40.classical-mechanics/10.main/textbook.fr.md

@@ -253,6 +253,16 @@ remember to replace (auto-tra) with your initials (YYY).
 [FR] transformation de Galilée
 [EN] Galileo's transformations
 
+$`\mathbf{\begin{cmatrix}
+\left \{
+t'=t \\
+x'=x-V_x\,t \\
+y'=y-V_y\,t \\   
+z'=z-V_z\,t 
+\end{cmatrix}
+\right.
+}`$
+
 
 *CLAPTMEC-FU-040* : 
 [ES] teorema de la suma de velocidades