Update cheatsheet.fr.md

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

@@ -83,6 +83,19 @@ RÉSUMÉ<br>
    \int_{t_1}^{t_2}\underbrace{\dfrac{dN}{N}}_{\text{de primitive }ln\,|N|}=\int_{t_1}^{t_2} r(t)\,dt
    end{align}`$
 
+  $`\displaystyle\begin{align}
+   \left.\dfrac{dN}{dt}\right\lvert_{\,\bigt}=r\,N(t)\quad &\Longrightarrow\quad
+   \left.\dfrac{dN}{N}\right\lvert_{\,\bigt}=r(t)\,dt\\
+   \\
+   &\Longrtightarrow\quad
+   \int_{t_1}^{t_2}\dfrac{dN}{N}=\int_{t_1}^{t_2} r(t)\,dt
+   end{align}`$
+   
+     $`\displaystyle\begin{align}
+   \left.\dfrac{dN}{dt}\right\lvert_{\,\bigt}=r\,N(t)\quad &\Longrightarrow\quad
+   \left.\dfrac{dN}{N}\right\lvert_{\,\bigt}=r(t)\,dt
+   end{align}`$
+