Update cheatsheet.fr.md

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

@@ -247,8 +247,8 @@ sur les condtions de mesure des durées et des longueurs?
 </span><span style="font-family:'Times New Roman';font-weight:bold;font-size:1.15rem;left;color:#bb3300"> longueur  l<sub>AB</sub>
 </span><span style="font-family:'Times New Roman';font-weight:bold;font-size:0.85rem;color:#6699ff"> entre ces deux points.</span>
 <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:1.15rem;text-align:left;color:#009900">$`\sqrt{(x_B-x_A)^2+(y_B-y_A)^2+(z_B-z_A)^2}`$}</span><br>
-<span style="font-family:'Times New Roman';font-weight:bold;font-size:1.15rem;text-align:left;color:#bbbbbb">dans des coordonnées cartésiennes $`(x,y,z)`$</span></p>
+<span style="font-family:'Times New Roman';font-weight:bold;font-size:0.85rem;text-align:left;color:#009900">$`l_{AB}=\sqrt{(x_B-x_A)^2+(y_B-y_A)^2+(z_B-z_A)^2}`$</span><br>
+<span style="font-family:'Times New Roman';font-weight:bold;font-size:1.15rem;text-align:left;color:#bbbbbb">en coordonnées cartésiennes $`(x,y,z)`$</span></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 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>