First major update of src/2_coordinates.md

src/2_coordinates.md

@@ -358,22 +358,22 @@ We have discussed four different coordinate systems:
 2.  !!! tip "Polar coordinates" 
     $${\bf r} = (r, \phi).$$ This system can be used in two
     dimensions. It is particularly suitable for systems with circular symmetry or functions
-    given in terms of these coordinates. \\
+    given in terms of these coordinates. <br/>
     Infinitesimal distance: $$ds^2 = dr^2 + r^2 d\phi^2.$$
     Infinitesimal area: $$dA = r dr d\varphi.$$
 
 3.  !!! tip "Cylindrical coordinates" 
     $${\bf r} = (r, \phi, z).$$ This system can be
     used in three dimensions. It is particularly suitable for systems with axial symmetry
-    or functions given in terms of these coordinates.
+    or functions given in terms of these coordinates. <br/>
     Infinitesimal distance: $$ds^2 = dr^2 + r^2 d\phi^2 + dz^2.$$
-    Infinitesimal volume:: $$dV = r dr d\varphi dz.$$
+    Infinitesimal volume: $$dV = r dr d\varphi dz.$$
 
 4.  !!! tip "Spherical coordinates" 
     $${\bf r} = (r, \theta, \phi).$$ This sysytem can be
     used in three dimensions. It is particularly suitable for systems with spherical
     symmetry or functions given in terms of these coordinates.
-    Infinitesimal distance:
+    Infinitesimal distance: <br/>
     $$ds^2 =r^2 (\sin^2 \theta d\phi^2 + d\theta^2) +  dr^2 .$$
     Infinitesimal volume:
     $$dV = r^2 \sin(\theta) dr d\theta d\varphi.$$