* math.c (math_cbrt): [DOC] Fix domain and codomain.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@49973 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

math.c

@@ -658,9 +658,9 @@ math_sqrt(VALUE obj, VALUE x)
  *
  *  Returns the cube root of +x+.
  *
- *  Domain: [0, INFINITY)
+ *  Domain: (-INFINITY, INFINITY)
  *
- *  Codomain:[0, INFINITY)
+ *  Codomain: (-INFINITY, INFINITY)
  *
  *    -9.upto(9) {|x|
  *      p [x, Math.cbrt(x), Math.cbrt(x)**3]