Chapter 4, Problem 12RE

To determine

To analyze: the given polynomial function

Answer to Problem 12RE

  

Explanation of Solution

Given:

  $f\left(x\right)=x\left(x-2\right)\left(x-4\right)$

Calculation:

Let us consider the following polynomial function,

  $f\left(x\right)=x\left(x-2\right)\left(x-4\right)$

Analyse the graph of the given function.

For this follow the following steps:

Step 1:Determination of the end behaviour of the graph of the function.

The end behaviour of the graph of a function is similar to the leading term of the function. So, first of all determine the degree of the function.

So,

  $\begin{array}{l}f\left(x\right)=x\left(x-2\right)\left(x-4\right)\hfill \\ \begin{array}{l}=\left(x^2-2x\right)\left(x-4\right)\\ =x^3-2x^2-4x^2+8x\end{array}\hfill \\ =x^3-6x^2+8x\hfill \end{array}$

Here, the degree of the polynomial is 3. So, the graph off behaves like

  $y=x^3$ for large values of $\left|x\right|$ .

Step 2:

Graph the function using a graphing utility.

Plot the given function.

  

Step 3: Next, approximate the x and the y intercepts of the graph.

From the graph, the graph passes through zero, so the y -intercept is at $y=0$ .

Also, the graph intersects the x -axis at 3 points, $x=0,x=2\text{ and }x=4$ .

Step 4:

Create a table to find points on the graph around each x intercept.

  

Step 5: Approximate the turning points of the graph.

From the graph off , f has two turning points.

Using MAXIMUM, one turning point is at $\left(0.82,\text{ 3}\text{.1}\right)$ , using MINIMUM; the other turning point is at $\left(3.29,-3.08\right)$ .

Step 6:

Complete the graph using all the above information.

  

Step 7:

Determine the range and domain of the function.

Domain and range of the function are the set of all real numbers. So,

  $\begin{array}{l}\text{Domain}=\left(-\infty ,\infty \right)\hfill \\ \text{Range}=\left(-\infty ,\infty \right)\hfill \end{array}$

Step 8:

Determine where the function is increasing and where it is decreasing.

From the graph, the function is increasing in the interval $\left(-\infty ,0.82\right)$ and $\left(3.29,\infty \right)$ . The function is decreasing in the interval $\left(0.82,3.29\right)$ .

Conclusion:

Therefore, the polynomial function $f\left(x\right)=x\left(x-2\right)\left(x-4\right)$ is analysed with graph.