DOC: Fix math block in hermmulx, lagmulx (numpy#20261)

The math expression needs to be indented, Otherwise it is seen as being
outside the directive and not rendered.

Author: Carreau

numpy/polynomial/hermite.py

@@ -419,7 +419,7 @@ def hermmulx(c):
 
     .. math::
 
-    xP_i(x) = (P_{i + 1}(x)/2 + i*P_{i - 1}(x))
+        xP_i(x) = (P_{i + 1}(x)/2 + i*P_{i - 1}(x))
 
     Examples
     --------

numpy/polynomial/hermite_e.py

@@ -414,7 +414,7 @@ def hermemulx(c):
 
     .. math::
 
-    xP_i(x) = (P_{i + 1}(x) + iP_{i - 1}(x)))
+        xP_i(x) = (P_{i + 1}(x) + iP_{i - 1}(x)))
 
     Examples
     --------

numpy/polynomial/laguerre.py

@@ -414,7 +414,7 @@ def lagmulx(c):
 
     .. math::
 
-    xP_i(x) = (-(i + 1)*P_{i + 1}(x) + (2i + 1)P_{i}(x) - iP_{i - 1}(x))
+        xP_i(x) = (-(i + 1)*P_{i + 1}(x) + (2i + 1)P_{i}(x) - iP_{i - 1}(x))
 
     Examples
     --------