Update textbook.en.md

12.temporary_ins/05.coordinates-systems/30.cylindrical-coordinates/10.main/textbook.en.md

@@ -86,7 +86,7 @@ The cylindrical coordinates are ordered and noted $`(\rho,\varphi,z)`$.
 For any point $`M`$ in space:
 
 \- The $`\rho_M`$ coordinate of the point $`M`$ is the nonalgebraic distance $`Om_{xy}`$
-between point $`O`$ and point $ m_{xy}`$. <br>
+between point $`O`$ and point $`m_{xy}`$. <br>
 \- The coordinate $`\varphi_M`$ of the point $`M`$ is the nonalgebraic angle
 $`\widehat{xOm_{xy}}`$ between the axis $`Ox`$ and the half-line $`Om_ {xy}`$,
 the direction of rotation being such that the trihedron $`(Ox,Om_{xy},Oz)`$ is a direct trihedron. <br>