Functions f and g are defined by

\(f(x) = 2x^2 + 8x + 1\) for \(x \in \mathbb{R}\),

\(g(x) = 2x - k\) for \(x \in \mathbb{R}\),

where \(k\) is a constant.

(ii) In the case where \(k = -9\), find the set of values of \(x\) for which \(f(x) < g(x)\).

(iii) In the case where \(k = -1\), find \(g^{-1}f(x)\) and solve the equation \(g^{-1}f(x) = 0\).

(iv) Express \(f(x)\) in the form \(2(x + a)^2 + b\), where \(a\) and \(b\) are constants, and hence state the least value of \(f(x)\).