Update cheatsheet.fr.md

12.temporary_ins/40.classical-mechanics/20.n2/10.framework-of-classical-mechanics-2/20.overview/cheatsheet.fr.md

@@ -252,16 +252,12 @@ $`\color{green}{l_{AB}=\sqrt{(x_B-x_A)^2+(y_B-y_A)^2+(z_B-z_A)^2}}`$
 <p style="font-family:'Times New Roman';font-weight:bold;font-size:1.15rem;text-align:left;color:#bbbbbb">un <span style="color:#0066cc"> invariant temporel<br>
 <span style="font-family:'Times New Roman';margin-left:30px;font-weight:bold;font-size:0.85rem;text-align:right;color:#6699ff">entre deux instants t<sub>1</sub> et t<sub>2</sub> du 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"> durée  Δt<sub>1\,2</sub></sub></span>
+</span><span style="font-family:'Times New Roman';font-weight:bold;font-size:1.15rem;left;color:#bb3300"> durée  Δt<sub>1 2</sub></sub></span>
 <span style="font-family:'Times New Roman';font-weight:bold;font-size:0.85rem;color:#6699ff"> entre ces deux instants.</span>
-<span style="font-family:'Times New Roman';font-weight:bold;font-size:1.15rem;text-align:left;color:#bbbbbb">d'expression, avec $`t_2 > t_1`$</span></p>
-$`\color{green}{\Delta t_{1\,2}=t_2-t_1}`$</p>
+<span style="font-family:'Times New Roman';font-weight:bold;font-size:1.15rem;text-align:left;color:#bbbbbb">d'expression</span></p>
+$`\color{green}{|\Delta t_{1\,2}=t_2-t_1|=\sqrt{(t_2-t_1}^2}}`$</p>
 <hr width=100% size=6px border-style="solid" color=#00bb33>
 
-$`\color{green}{l_{AB}=\sqrt{(x_B-x_A)^2+(y_B-y_A)^2+(z_B-z_A)^2}}`$
-
-durée  t<sub>2</sub> - t<sub>1</sub>
-
 
    ![](https://m3p2.com/temporary_ins/relativity/n2/an-euclidian-space-time/overview/train-speed-0-persons-ABD_L1200.jpg)