$解:(3)當 -1<a<0,b<0時$
$不等式變形得:$
$\begin{cases}{\ x>\frac{1}{a}}\\{x>-1}\end{cases}$
$解得: x\gt -1$
$當 -1<a<0,b> 0時$
$不等式變形得:$
$\begin{cases}{x>\frac{1}{a}}\\{x<-1}\end{cases}$
$解得: \frac {1}{a}<x<-1$
$當 0<a<1,b<0時$
$不等式變形得:\ $
$\begin{cases}{x<\frac{1}{a}\ }\\{x>-1}\end{cases}$
$解得: -1<x<\frac {1}{a}\ $
$當 0<a<1,b>0 時$
$不等式變形得:$
$\begin{cases}{x<\frac{1}{a}}\\{x<-1}\end{cases}$
$解得: x\lt -1. $