Update textbook.en.md

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

@@ -55,7 +55,7 @@ Reference frame: Cartesian coordinate system $ `(O, x, y, z)` $
 ! can give :
 
 The cylindrical coordinates are defined from a Cartesian coordinate system, i.e.
-\- 1 point $`O`  origin of space. <br>
+\- 1 point $`O`$ origin of space. <br>
 \- 3 axes named $`Ox, Oy, Oz`$, intersecting at $`O`$, orthogonal 2 to 2. <br>
 \- 1 unit of length. <br>
 
@@ -77,7 +77,7 @@ a *direct trihedron*.<br>
 \- The **coordinate $`z_M`$** of the point $`M`$ is the *algebraic distance $`\overline {Om_z}`$*
 between the point $`O`$ and the point $`m_z`$.
 
-**$`\rho_M=\overline{Om_ {xy}}`$, $`\varphi_M = \widehat{xOm_y}`, $`z_M =Om_z`$**
+**$`\rho_M=\overline{Om_ {xy}}`$, $`\varphi_M = \widehat{xOm_y}`$, $`z_M =Om_z`$**
 
 ! can give :