Update cheatsheet.fr.md

12.temporary_ins/10.electrostatics-vacuum/20.causes-stationary-electric-field/20.overview/cheatsheet.fr.md

@@ -539,6 +539,7 @@ figure
 ! $`E_z = \dfrac{\dens^{1D}}{2\epsilon_0}\cdot\dfrac{R\,z}{(R^2+z^2)^{\,3/2}}`$<br>
 ! <br>
 ! devient <br>
+! <br>
 ! $`dE_z = \dfrac{\dens^{2D}}{2\epsilon_0}\cdot\dfrac{\rho\,z}{(\rho^2+z^2)^{\,3/2}}\,d\rho`$ <br>
 ! <br>
 ! $`\hspace{1cm} = \dfrac{\dens^{2D}\,z}{2\epsilon_0}\cdot \rho\,(\rho^2+z^2)^{-\,3/2}\,d\rho`$<br>
@@ -553,7 +554,8 @@ figure
 !
 ! $`\displaystyle E_z = \int_{\rho = 0}^R \dfrac{\dens^{2D}\,z}{2\epsilon_0}\cdot \rho\,(\rho^2+z^2)^{-\,3/2}\,d\rho`$<br>
 ! <br>
-! $`\displaystyle \hspace{1cm} =  \dfrac{\dens^{2D}\,z}{2\epsilon_0} \int_{\rho = 0}^R\dfrac{1}{2}\,2\rho\,(\rho^2+z^2)^{-\,3/2}\,d\rho`$<br>
+! $`\displaystyle \hspace{1cm} =  \dfrac{\dens^{2D}\,z}{2\epsilon_0} \int_{\rho = 0}^R\dfrac{1}{2}\times
+! \underbrace{2\rho}_{u^{\,'}}\,\underbrace{(\rho^2+z^2)^{-\,3/2}}_{u^n}\,d\rho`$<br>
 ! <br>
 ! $`\displaystyle \hspace{1cm} =  \dfrac{\dens^{2D}\,z}{2\epsilon_0} \big[\underbrace{\dfrac{1}{2}\times\dfrac{1}{-3/2+1}}
 ! _{=\frac{1}{2}\,\times \,(-2) \,=\, -1}(\rho^2+z^2)^{-\,1/2}\big]_0^R`$<br>