Update cheatsheet.fr.md

12.temporary_ins/32.sets-systems/30.n3/20.systems/20.overview/cheatsheet.fr.md

@@ -85,7 +85,7 @@ RÉSUMÉ<br>
   $`\displaystyle\begin{align}
    \left.\dfrac{dN}{dt}\right\lvert_{\,\bigt} =r\,N(t)&\quad \Longrightarrow\quad\left.\dfrac{dN}{N}\right\lvert_{\,\bigt}=r\,dt\\
    \\
-   &\Longrightarrow\quad\left.\dfrac{dN}{N}\right\lvert_{\,\bigt}=r(t)\,dt\\
+   &\int_{N(t_1)}^{N(t_2)}\dfrac{dN}{N}=\int_{t_1}^{t_2} r\,dt\\
    \\
    &\Longrightarrow\quad
    \big[\,ln\,|N|\,\big]_{N(t_1)}^{N(t_2)}=\int_{t_1}^{t_2} r \,\big[\,t\,\big]_{t_1}^{t_2}