Update textbook.fr.md

00.brainstorming-pedagogical-teams/40.collection-existing-pedagogical-content/05.classical-mechanics/vector-analysis/textbook.fr.md

@@ -68,6 +68,8 @@ mathematical expressions. Example :
 $`\Longrightarrow \quad\forall \overrightarrow{V}\in\mathcal{P}`$$`\quad\exists ! (\alpha,\beta)\in\mathbb{R}^2`$$`\quad
 \overrightarrow{V}=\alpha\cdot\overrightarrow{a}+\beta\cdot\overrightarrow{b}`$
 
+https://en.wikipedia.org/wiki/ISO_31-11
+
 ---
 
 ## Colección de elementos del curso: conceptos, vocabulario y ecuaciones / Collection d'éléments de cours : Concepts, vocabulaire et équations / Collection of Course Elements: Concepts, Vocabulary and Equations
@@ -258,6 +260,13 @@ $`M=M(\alpha, \beta, \gamma)`$.
 [EN] There are *several possible ways to define spatial coordinates*: We speak of 
 ** coordinate systems**.
 
+* [ES]
+[FR]
+[EN] Specific alphanumeric characters are defined for some widely used coordinate systems :<br>
+\- cartesian : $`(x, y, z)`$ or $`(O, x_1, x_2, x_3)`$<br>
+\- cylindric : $`(\rho, \phi, z)`$ or $`(r, \phi, z)`$<br>
+\- spheric : $`(x, y, z)`$ or $`(O, x_1, x_2, x_3)`$<br>
+
 
 #### Características de una base / Caractéristiques d’une base et d’un repère / Characteristics of a base