There are only two things which restrict the domain 
or range of a function in ordinary algebra.

1.  Denominators which must never be 0.
2.  Even root radicands which must never be negative.

If there are no denominators or even root radicands 
which contain variables then the domain is always
(-¥, ¥)

             1
y = f(x) = ----
            x4

has a denominator with a variable, so we must 
require that x4 ¹ 0, or x ¹ 0

So the domain is 

      (-¥, 0) È (0, ¥)

To find the range, we solve the equation for x, 
and use the same criteria for y.

             1
       y = ----
            x4

Multiply both sides by x4

     x4y = 1

            1 
      x4 = ---
            y

             1
      x =  -----
            4Öy

This is an even root radical, therefore its radicand, y
must not be negative. Since it is also in a denominator
it must not be 0 either.  Therefore it must by greater
than 0, or y > 0.  Therefore the range is

       (0, ¥)

Edwin