9. The solution to the equation $\frac{x+1}{x+2}+\frac{x+8}{x+9}=\frac{x+2}{x+3}+\frac{x+7}{x+8}$ is
9. $-\frac{11}{2}$.

Hint: The original equation can be transformed into
$$
(x+2)(x+3)=(x+8)(x+9) .
$$