Update cheatsheet.fr.md

12.temporary_ins/07.geometry-coordinates-prop2/40.n4/20.overview/cheatsheet.fr.md

@@ -1007,6 +1007,17 @@ en ce point $`\mathbf{e_a}(\lambda)`$.
 <br>
 $`\mathbf{v}(\lambda) = v^a(\lambda)\,\mathbf{e_a}(\lambda)`$
 
+$`\begin{align}\Large{\dfrac{d\mathbf{v}}{d\lambda}}&=\dfrac{d}{d\lambda}\,\bigg(v^a\,\mathbf{e_a}\bigg)\\
+\\
+=\dfrac{dv^a}{d\lambda}\,\mathbf{e_a}+v^a\,\dfrac{d\mathbf{e_a}}{d\lambda}\\
+\\
+=\dfrac{dv^a}{d\lambda}\,\mathbf{e_a}+v^a\,\underbrace{\dfrac{d\mathbf{e_a}}{dx^b}}{\color{brown}{=\,\Gamma_{ab}{\;c}}}
+\,\dfrac{d\mathbf{x^b}}{d\lambda}\\
+\\
+=\dfrac{dv^a}{d\lambda}\,\mathbf{e_a}+v^a\,\underbrace{\dfrac{d\mathbf{e_a}}{dx^b}}{\color{brown}{=\,\Gamma_{ab}{\;c}}}
+\,\dfrac{d\mathbf{x^b}}{d\lambda}\\
+\end{align}`$
+