Update cheatsheet.fr.md

12.temporary_ins/69.waves/20.n2/20.overview/cheatsheet.fr.md

@@ -367,8 +367,13 @@ $`\begin{align}
 <br>
 $`\begin{align}
 \mathscr{v}_{propag.}\,t_2' - \mathscr{v}_{propag.}\,t_2 &= \mathscr{v}_{propag.}\,t_1' -  \mathscr{v}_{propag.}\,t_1\\
-& \hspace{1cm} + \mathscr{v}_{source}\,t_2 - \mathscr{v}_{source}\,t_1\\
-& \hspace{2cm} +\mathscr{v}_{capteur}\,t_2' - \mathscr{v}_{capteur}\,t_1'
+& \hspace{0.8cm} + \mathscr{v}_{source}\,t_2 - \mathscr{v}_{source}\,t_1\\
+& \hspace{1.6cm} +\mathscr{v}_{capteur}\,t_2' - \mathscr{v}_{capteur}\,t_1'
+\end{align}`$
+
+$`\begin{align}
+&\mathscr{v}_{propag.}\,t_2' - \mathscr{v}_{propag.}\,t_1' - \mathscr{v}_{capteur}\,t_2'+ \mathscr{v}_{capteur}\,t_1'\\
+& \hspace{1.5cm} =  \mathscr{v}_{propag.}\,t_2 -  \mathscr{v}_{propag.}\,t_1 + \mathscr{v}_{source}\,t_2 - \mathscr{v}_{source}\,t_1 
 \end{align}`$
 
 ! sous chapitre ## : Le phénomène de réflexion