$f(x) = \frac{{\alpha x + b}}{{cx + d}} \to g(x) = \frac{{cx + d}}{{\alpha x + b}}$
$\mathop {\lim }\limits_{x \to - \infty } \frac{{\frac{{\alpha x + b}}{{cx + d}}}}{{\frac{{ - bx + d}}{{\alpha x - c}}}} = \mathop {\lim }\limits_{x \to + \infty } \frac{{\frac{{ - bx + d}}{{\alpha x - c}}}}{{\frac{{cx + d}}{{\alpha x + b}}}}$
$ \Rightarrow \frac{{{\alpha ^2}}}{{ - bc}} = \frac{{ - \alpha b}}{{\alpha c}} \Rightarrow {\alpha ^2} = {b^2}$
$ \Rightarrow \alpha = \pm b$
$\mathop {\lim }\limits_{x \to {0^ + }} {f^{ - 1}}(x) = \lim \frac{{ - dx + b}}{{cx - \alpha }} = \frac{{ - b}}{\alpha }$
$ - \frac{b}{\alpha } = 1$