Chapter 3: Problem 22
Sketch the graph of the polynomial function. Make sure your graph shows all intercepts and exhibits the proper end behavior. $$P(x)=(x-3)^{2}(x+1)^{2}$$
Short Answer
Expert verified
The polynomial has roots at x = 3 and x = -1, both with even multiplicity, a y-intercept at (0, 9), and the graph rises on both ends.
Step by step solution
01
Identify the Roots
The given polynomial is \( P(x) = (x-3)^{2}(x+1)^{2} \). The roots of the polynomial are the values of \( x \) that make \( P(x) = 0 \). From the factors, we identify the roots as \( x = 3 \) and \( x = -1 \). Each has multiplicity 2.
02
Determine the Y-intercept
To find the y-intercept, substitute \( x = 0 \) into the polynomial: \( P(0) = (0-3)^{2}(0+1)^{2} = 9 \times 1 = 9 \). Thus, the y-intercept is \( (0, 9) \).
03
Analyze the End Behavior
The polynomial \( P(x) = (x-3)^{2}(x+1)^{2} \) has a degree of 4 (since each squared factor contributes two to the degree). As a positive leading-coefficient, even-degree polynomial, the graph will rise to positive infinity on both sides as \( x \to \pm \infty \).
04
Consider Multiplicities at Roots
Both roots \( x = 3 \) and \( x = -1 \) have even multiplicities (2). Therefore, at these points, the graph will touch the x-axis and turn around (rather than crossing it).
05
Sketch the Graph
To sketch the graph, plot the x-intercepts at \( (3, 0) \) and \( (-1, 0) \), and the y-intercept at \( (0, 9) \). Show the function touching and turning at the x-intercepts due to the even multiplicity of roots. Begin the graph from the upper left, touch the x-axis at \( x = -1 \), rise to the y-intercept at \( x = 0 \), descend to touch the x-axis again at \( x = 3 \), and then rise to the upper right.
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Roots of Polynomial
Roots of a polynomial are values of \( x \) for which the polynomial equals zero. Think of them as the points where the graph of the polynomial touches or crosses the x-axis. In the polynomial \( P(x) = (x-3)^{2}(x+1)^{2} \), it's factored into two products. This allows us to find the roots directly by solving each factor for zero:
- \( x - 3 = 0 \Rightarrow x = 3 \)
- \( x + 1 = 0 \Rightarrow x = -1 \)
Y-intercept
The y-intercept of a graph is where the graph crosses the y-axis. It is found by setting \( x = 0 \) and solving for \( y \). For \( P(x) = (x-3)^{2}(x+1)^{2} \), substituting \( x = 0 \) gives:\[ P(0) = (0-3)^{2} (0+1)^{2} = 9 \times 1 = 9 \]Thus, the y-intercept is \( (0, 9) \). This point is critical in plotting the polynomial as it ensures that the graph is positioned correctly in relation to the y-axis. Every polynomial has exactly one y-intercept since it is only dependent on the constant term when the polynomial is expressed in standard form.
End Behavior
End behavior describes how the polynomial behaves as \( x \) approaches positive or negative infinity. For \( P(x) = (x-3)^{2}(x+1)^{2} \), the degree of the polynomial is 4. Each squared factor contributes 2 to this degree, making it even. An even-degree polynomial with a positive leading coefficient (like ours) has ends that go to infinity in the same direction:
- As \( x \to +\infty \), \( P(x) \to +\infty \)
- As \( x \to -\infty \), \( P(x) \to +\infty \)
Multiplicity of Roots
Multiplicity of a root refers to how many times a particular root is repeated in the polynomial equation. For \( P(x) = (x-3)^{2}(x+1)^{2} \), each root, \( x = 3 \) and \( x = -1 \) , is repeated twice, giving them a multiplicity of 2.Multiplicity affects whether a graph crosses or merely touches the x-axis at the root:
- Roots with even multiplicity (like in our polynomial) cause the graph to touch the x-axis and turn around without crossing it.
- Roots with odd multiplicity cross the x-axis and do not turn around.