9. Given $f(x)=\frac{b x+1}{2 x+a} \quad(a, b$ are constants, $a b \neq 2)$. If $f(x) \cdot f\left(\frac{1}{x}\right)$ $=k$, then $k=$ $\qquad$ ; If $f[f(1)]=\frac{k}{2}$, then $a=$ $\qquad$ $b=$
\[
\begin{aligned} 
k & =\frac{1}{4}, b \\ 
& =-\frac{7}{2}, a=-7 
\end{aligned}
\]