A function is said to be increasing when, as the x-values increase (from left to right), the values of f(x) increase. Conversely, a function is said to be decreasing when, as x increases, f(x) decreases. The graph below shows increasing intervals with green arrows and decreasing intervals with red arrows.
The function above contains two increasing intervals and one decreasing interval. To describe each, use the x-values. Commonly a point where a function has a relative maximum or a relative minimum is neither included in an increasing nor a decreasing interval.
For some functions, their graphs extend infinitely in the vertical direction. For these graphs, there are no highest or lowest points. However, it's possible for these functions to have relative minimum or relative maximum values. A relative minimum is the lowest point for a region of the graph. Similarly, a relative maximum is the highest point for a region of the graph.
Relative minimums and maximums of polynomial functions are also called turning points. This is because a function's graph turns from increasing to decreasing, or vice versa, at these points.
The graph of a polynomial function of degree n can have at most n−1 turning points. The function shown is a 3rd degree polynomial and has 2 turning points.Furthermore, a polynomial function with n real zeros must have at least n−1 turning points.
If a function has a symmetry, it is either even or odd. The symmetry is even when the graph is symmetric with respect to the y-axis, and odd when it's symmetric about the origin.
We can determine if a function has even or odd symmetry, using its function rule and the following relationships.
Simplify power and product
The figure below shows the graph of a polynomial function.
Use the graph to determine
Draw a graph of a polynomial function, f(x), having these characteristics.
Two of these points, (-3,0) and (3,0), lie in intervals where f(x) is decreasing. The third point, (1,0), is instead in an interval where the function is increasing. Using this, we can draw short sections of the function through the zeros.
When a function changes from increasing to decreasing, or vice versa, it does so at a turning point. From the given information, these changes occur at x=-1 and x=2. We can extend the already-drawn sections to these x-values.
Note that, because we don't have the exact coordinates of the turning point, their position is approximate. The function is decreasing both when x<-1 and when x>2. Since we know that, we can now draw the rest of the graph.