9 The functions f and g are defined for all real values of \(x\) by $$\mathrm { f } ( x ) = 4 x ^ { 2 } - 12 x \quad \text { and } \quad \mathrm { g } ( x ) = a x + b$$ where \(a\) and \(b\) are non-zero constants.

1. Find the range of f .
2. Explain why the function \(f\) has no inverse.
3. Given that \(\mathrm { g } ^ { - 1 } ( x ) = \mathrm { g } ( x )\) for all values of \(x\), show that \(a = - 1\).
4. Given further that \(\operatorname { gf } ( x ) < 5\) for all values of \(x\), find the set of possible values of \(b\).