docs: fixing math markup

docs/en/stereonet.rst

@@ -20,9 +20,9 @@ In most cases it is preferable to use a projection that optimises equal area, be
 
     Small circles (all 10° radius) make it easier to see that area is preserved reasonably well across all orientations. Angles are slightly distorted and make the circles appear as ellipses.
 
-The x-axis (horizontal) and y-axis (vertical) coordinates 
+The x-axis (horizontal) and y-axis (vertical) coordinates of a latitude-longitude measurement can be calculated using the following formula:
 
-  .. raw:: latex html
+.. math::
 
     x = Rk \cos(\phi) \sin(\lambda - \lambda_{0}
     y = Rk \sin(\phi)
@@ -33,7 +33,7 @@ The x-axis (horizontal) and y-axis (vertical) coordinates
 
 With k equal to:
 
-  .. raw:: latex html
+.. math::
 
     k = \frac{2 k_{0}}{1 + \cos(\phi) \cos(\lambda - \lambda_{0}}