Chapter 5: Problem 51
For the following exercises, graph the polynomial functions using a calculator. Based on the graph, determine the intercepts and the end behavior.For the following exercises, make a table to confirm the end behavior of the function. $$ f(x)=x^{3}(x-2) $$
Short Answer
Expert verified
The intercepts are \((0,0)\) and \((2,0)\). Both ends rise.
Step by step solution
01
Factor the Polynomial
The given polynomial function is already factored: \[ f(x) = x^3 (x - 2) \]. This will help us easily determine the roots and analyze the graph.
02
Determine the Intercepts
To find the **x-intercepts**, set the polynomial equation to zero:\[ x^3 (x - 2) = 0 \].This gives us the intercepts at \(x = 0\) (with multiplicity 3) and \(x = 2\). The **y-intercept** occurs when \(x = 0\), hence the point is \((0, 0)\).
03
Use a Calculator for Graph
Using a graphing calculator, plot the function \(f(x) = x^3 (x - 2)\). Observe the overall shape and direction of the graph.
04
Analyze End Behavior
Identify how the function behaves as \(x\) approaches infinity and negative infinity.Due to the leading term \(x^4\), as \(x \to \infty\), \(f(x) \to \infty\) and as \(x \to -\infty\), \(f(x) \to \infty\).
05
Create a Table for Confirmation
Make a table with values of \(x\) and corresponding \(f(x)\) to confirm the end behavior:\[\begin{array}{|c|c|}\hline x & f(x) \\hline -3 & 81 \ -2 & -32 \ -1 & -3 \ 0 & 0 \ 1 & 1 \ 2 & 0 \ 3 & 81 \\hline\end{array}\]The table supports that as \(x\) approaches large positive or negative values, \(f(x)\) values are increasingly positive.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Intercepts in Graphs
Intercepts are crucial in understanding the behavior and position of a polynomial function on a graph. They provide us with information on where the function intersects the x-axis and the y-axis.
- X-intercepts: These are the points where the graph crosses the x-axis. To find them for the polynomial \(f(x) = x^3(x-2)\), we set the polynomial equal to zero: \(x^3(x-2) = 0\). Solving for \(x\) gives the roots \(x = 0\) and \(x = 2\). The intercept \(x = 0\) has a multiplicity of 3, suggesting the graph is tangent to the x-axis at this point.
- Y-intercept: This is where the graph crosses the y-axis, found by evaluating the function at \(x = 0\). For \(f(0)\), we substitute zero into the equation, resulting in \(f(0) = 0\). Thus, the graph intersects the y-axis at the origin, \((0, 0)\).
End Behavior
End behavior describes how a polynomial function behaves as the input values become very large or very small.For our function \(f(x) = x^3(x - 2)\), the degree of the polynomial is 4 (when expanded, the leading term is \(x^4\)). The degree of the polynomial plays a critical role in determining end behavior:
- Since the leading term \(x^4\) is positive and the degree is even, as \(x \to +\infty\), \(f(x) \to +\infty\). Similarly, as \(x \to -\infty\), \(f(x) \to +\infty\).
Graphing Calculators
Graphing calculators are invaluable tools for students when exploring polynomial functions. They can quickly plot the graph of a function and provide visual insight into intercepts and end behavior. To graph the function \(f(x) = x^3(x - 2)\):
- Input the function into the calculator. Ensure you adjust your window settings appropriately to view the intercepts and the general shape.
- Identify the key features of the graph, such as where it crosses the axes and the shape in relation to the end behavior.
Factoring Polynomials
Factoring is a central technique in handling polynomial functions. It simplifies the solution of equations and aids in graphing.The given function \(f(x) = x^3(x - 2)\) is already factored, showcasing its roots clearly. Here are some benefits of factoring:
- Simplifies finding intercepts: By expressing \(f(x)\) as a product of its factors, we easily find the x-intercepts, as setting each factor to zero provides the intercepts directly.
- Aids in graph sketching: Knowing intercepts and factored form allows us to sketch the graph more intuitively, understanding points of tangency and how the graph moves between intercepts.