A function is called increasing when as the x-values increase, the values of f(x) also increase. On the other hand, a function is called decreasing when, as x increases, f(x)decreases. An increasing interval is an interval of the independent variable for an increasing function. A decreasing interval is an interval of the independent variable for a decreasing function.
A point where a function has a maximum or a minimum is neither included in an increasing or a decreasing interval.
The previous applet shows a function that contains two increasing intervals and one decreasing interval. Each can be described in terms of the x-values.
Although the entire graph cannot be seen, it is reasonable to assume that it continues in the same manner. In that case, for all x-values less than x=-2,f will be increasing. For all x-values greater than x=0,f will also be increasing.