Update textbook.fr.md

12.temporary_ins/40.classical-mechanics/40.n4/70.lagrangian-mechanics/07.coherence/textbook.fr.md

@@ -172,12 +172,12 @@ $`\displaystyle\;=\int_{\alpha_1}^{\alpha_2}\dfrac{d (uv)}{d\alpha}\,d\alpha
 <br>
 
 $`\dfrac{\partial\mathcal{L}}{\partial \dpt{x}_i} \cdot\delta \dpt{x}_i`$
-$`\;=\dfrac{\partial\mathcal{L}}{\partial \dpt{x}_i}\cdot\dfrac{d\,\partial x_i}{dt}`$
+$`\;=\dfrac{\partial\mathcal{L}}{\partial \dpt{x}_i}\cdot\dfrac{d\,\delta x_i}{dt}`$
 
 $`u=\dfrac{\partial \mathcal{L}}{\partial\dpt{q}}`$
 
-$`\quad=\dfrac{d}{dt}\bigg(\,\dfrac{\partial\mathcal{L}}{\partial \dpt{x}_i}\cdot \partial x_i\bigg)
--\dfrac{d}{dt}\bigg(\,\dfrac{\partial\mathcal{L}}{\partial \dpt{x}_i}\bigg)\cdot \partialx_i`$
+$`\quad=\dfrac{d}{dt}\bigg(\,\dfrac{\partial\mathcal{L}}{\partial \dpt{x}_i}\cdot \delta x_i\bigg)
+-\dfrac{d}{dt}\bigg(\,\dfrac{\partial\mathcal{L}}{\partial \dpt{x}_i}\bigg)\cdot \delta x_i`$