Update cheatsheet.fr.md

12.temporary_ins/44.relativity/20.n2/10.an-euclidian-space-time/20.overview/cheatsheet.fr.md

@@ -930,6 +930,22 @@ choix des coordonnées xyt pour la prochiane figure
 
 <br>  -->
 
+<p style="font-family:'Times New Roman';font-weight:bold;font-size:1.15rem;text-align:left;color:#009900">Tous les observateurs galiléens partagent</p>
+<hr width=100% size=6px border-style="solid" color=#00bb33>
+<p style="font-family:'Times New Roman';font-weight:bold;font-size:1.15rem;text-align:left;color:#bbbbbb">un <span style="color:#0066cc"> invariant spatio-temporel<br>
+<span style="font-family:'Times New Roman';margin-left:30px;font-weight:bold;font-size:0.85rem;text-align:right;color:#6699cc">entre deux évènements A et B de l'espace-temps </span><br>
+<span style="font-family:'Times New Roman';font-weight:bold;font-size:1.15rem;color:#bbbbbb">appelé 
+</span><span style="font-family:'Times New Roman';font-weight:bold;font-size:1.15rem;left;color:#bb3300"> interval  s<sub>AB</sub><br>
+<span style="font-family:'Times New Roman';font-weight:bold;font-size:1.15rem;text-align:left;color:#bbbbbb">d'expression</span>
+<span style="font-family:'Times New Roman';font-weight:bold;font-size:0.85rem;text-align:right;color:#009933">en coordonnées cartésiennes</span></p>
+$`\color{green}{s_{AB}=\sqrt{(\Delta t_{AB})^2+(\Delta l_{AB})^2(y_B-y_A)^2+(z_B-z_A)^2}}`$
+<p style="font-family:'Times New Roman';font-weight:bold;font-size:0.85rem;text-align:right;color:#009933">avec, en coordonnées spatiales cartésiennes</p>
+$`Delta l_{AB}=\sqrt{(x_B-x_A)^2+(y_B-y_A)^2+(z_B-z_A)^2}`$
+<p style="font-family:'Times New Roman';font-weight:bold;font-size:0.85rem;text-align:right;color:#009933">et</p>
+$`Delta l_{AB}=\sqrt{(t_B-t_A)^2}`$
+<hr width=100% size=6px border-style="solid" color=#00bb33>
+
+
 et autres figures à venir
 
 Chapitrage :