Chapter 5 Polynomial and Rational Functions
5.3 Graphs of Polynomial Functions
Learning Objectives
In this section, you will:
- Recognize characteristics of graphs of polynomial functions.
- Use factoring to find zeros of polynomial functions.
- Identify zeros and their multiplicities.
- Determine end behavior.
- Understand the relationship between degree and turning points.
- Graph polynomial functions.
- Use the Intermediate Value Theorem.
The revenue in millions of dollars for a fictional cable company from 2006 through 2013 is shown in Table 1.
| Year | 2006 | 2007 | 2008 | 2009 | 2010 | 2011 | 2012 | 2013 |
| Revenues | 52.4 | 52.8 | 51.2 | 49.5 | 48.6 | 48.6 | 48.7 | 47.1 |
Table 1.
The revenue can be modeled by the polynomial function
[latex]R\left(t\right)=-0.037{t}^{4}+1.414{t}^{3}-19.777{t}^{2}+118.696t-205.332[/latex]
where[latex]\,R\,[/latex]represents the revenue in millions of dollars and[latex]\,t\,[/latex]represents the year, with[latex]\,t=6\,[/latex]corresponding to 2006. Over which intervals is the revenue for the company increasing? Over which intervals is the revenue for the company decreasing? These questions, along with many others, can be answered by examining the graph of the polynomial function. We have already explored the local behavior of quadratics, a special case of polynomials. In this section we will explore the local behavior of polynomials in general.
Recognizing Characteristics of Graphs of Polynomial Functions
Polynomial functions of degree 2 or more have graphs that do not have sharp corners; recall that these types of graphs are called smooth curves. Polynomial functions also display graphs that have no breaks. Curves with no breaks are called continuous. Figure 1 shows a graph that represents a polynomial function and a graph that represents a function that is not a polynomial.
Recognizing Polynomial Functions
Which of the graphs in Figure 2 represents a polynomial function?
Show Solution
The graphs of[latex]\,f\,[/latex]and[latex]\,h\,[/latex]are graphs of polynomial functions. They are smooth and continuous.
The graphs of[latex]\,g\,[/latex]and[latex]\,k\,[/latex]are graphs of functions that are not polynomials. The graph of function[latex]\,g\,[/latex]has a sharp corner. The graph of function[latex]\,k\,[/latex]is not continuous.
Do all polynomial functions have all real numbers as their domain?
Yes. Any real number is a valid input for a polynomial function.
Using Factoring to Find Zeros of Polynomial Functions
Recall that if[latex]\,f\,[/latex]is a polynomial function, the values of[latex]\,x\,[/latex]for which[latex]\,f\left(x\right)=0\,[/latex]are called zeros of[latex]\,f.\,[/latex]If the equation of the polynomial function can be factored, we can set each factor equal to zero and solve for the zeros.
We can use this method to find[latex]\,x\text{-}[/latex]intercepts because at the[latex]\,x\text{-}[/latex]intercepts we find the input values when the output value is zero. For general polynomials, thi