Fix some typos in help text

Thanks to Doug Stewart for point these out.

inst/@sym/degree.m

@@ -20,7 +20,7 @@
 %% @documentencoding UTF-8
 %% @deftypefn  {Function File} {@var{n} =} degree (@var{p})
 %% @deftypefnx {Function File} {@var{n} =} degree (@var{p}, @var{x})
-%% Extract numerator and demoninator of symbolic expression.
+%% Return the degree of a polynomial expression.
 %%
 %% Examples:
 %% @example

inst/@sym/formula.m

@@ -17,7 +17,7 @@
 %% If not, see <http://www.gnu.org/licenses/>.
 
 %% -*- texinfo -*-
-%% @deftypefn {Function File} {@var{g}} formula (@var{f})
+%% @deftypefn {Function File} {@var{g} =} formula (@var{f})
 %% Return a symbolic expression for this object.
 %%
 %% For a @@sym, this simply returns the sym itself.  Subclasses

inst/@sym/numden.m

@@ -17,26 +17,25 @@
 %% If not, see <http://www.gnu.org/licenses/>.
 
 %% -*- texinfo -*-
+%% @documentencoding UTF-8
 %% @deftypefn  {Function File} {@var{n}, @var{d} =} numden (@var{x})
-%% Extract numerator and demoninator of symbolic expression.
+%% Extract numerator and denominator of symbolic expression.
 %%
 %% Examples:
 %% @example
 %% @group
 %% >> [n, d] = numden(sym(4)/5)
-%%    @result{}
-%%      n = (sym) 4
-%%      d = (sym) 5
+%%    @result{} n = (sym) 4
+%%    @result{} d = (sym) 5
 %% @end group
 %% @end example
 %%
 %% @example
 %% @group
 %% >> syms x y
 %% >> [n, d] = numden((x+y)/sin(x))
-%%    @result{}
-%%      n = (sym) x + y
-%%      d = (sym) sin(x)
+%%    @result{} n = (sym) x + y
+%%    @result{} d = (sym) sin(x)
 %% @end group
 %% @end example
 %%

inst/@symfun/formula.m

@@ -17,7 +17,8 @@
 %% If not, see <http://www.gnu.org/licenses/>.
 
 %% -*- texinfo -*-
-%% @deftypefn {Function File} {@var{g}} formula (@var{f})
+%% @documentencoding UTF-8
+%% @deftypefn {Function File} {@var{g} =} formula (@var{f})
 %% Return a symbolic expression for this symfun.
 %%
 %% This returns the expression that defines the function given by