if they're asking for the range then there is no upper bound on what the y values can be since the limit as x goes to infinity is infinity
this thing is clearly a parabola which is concave up, i am not sure why the book gives that answer... are you sure you're looking at the right problem
Sorry this is wrong. The given function is a typical parabola. The domain is all real numbers.
Furthermore, if you complete the square you get and the clearly the range has nothng to do with the given answer either. As has already been remarked, IF the posted question is accurate then the book's answer is wrong.