Example 3. Solve the inequality

$$
|x|<-x^{2}+x+6 .
$$
Solution. The given inequality is equivalent to the combination of two systems:

$$
\left\{\begin{array} { l } 
{ x 0$ it is equivalent to the system

$$
\left\{\begin{array}{r}
f(x)<a \\
-f(x)<a
\end{array}\right.
$$