To find the range of a function, here are the five basic steps:

1
Label the function as y = f(x).
2
Express x as a function of y.
3
Find all values of y where f(y) is defined.
4
Eliminate the values of y that will make the function undefined.
5
Write the range.

Create a named range from selected cells in a worksheet

1
Select the range you want to name, including the row or column labels.
2
Click Formulas > Create from Selection.
3
In the Create Names from Selection dialog box, select the checkbox (es) depending on the location of your row/column header. ...
4
Click OK.