Third-degree polynomial usually has 1 relative maximum and 1 relative minimum, or they don't have a relative maximum or minimum. Looking at the graph we can see that there's one relative maximum and one relative minimum.
The relative minimum is near x = 1, and the relative maximum is near x = 3. There are 1 relative maximum and 1 relative minimum
The increasing interval will be the interval between the relative minimum and the relative maximum, then, approximately the interval (1.2, 2.8), that's the increasing interval
[tex](1.2,2.8)[/tex]
The decreasing interval will be any other value removing the increasing interval, then, we can write the decreasing interval as
[tex](-\infty,1.2\rbrack\cup\lbrack2.8,+\infty)[/tex]
