9. Let the quadratic function $f(x)=a x^{2}+b x+c$, when $x=-2$, it has a maximum value of $a^{2}$, and its graph passes through the point $(-1,6)$, then $\frac{a+c}{b}=$ $\qquad$ .
9. $\frac{1}{2}$ According to the problem, $-\frac{b}{2 a}=-2 \cdot \frac{4 a c-b^{2}}{4 a}=a^{2}, 6=a-b+c$, and $a<0$, we can solve to get $a=-3, b=-12, c=-3$.