Q. The function g is defined by \(g(x)=x(x-2)(x+6)^2\).
Answer
\[g(x)=x(x-2)(x+6)^2\]
\[g'(x)=2(x+6)(2x^2+3x-6)\]
\[g'(x)=0\ \text{gives}\ x=-6\ \text{or}\ 2x^2+3x-6=0,\ \text{so}\ x=\frac{-3\pm\sqrt{57}}{4}\approx -2.63745,\;1.13745\]
\[g”(x)=12(x^2+5x+2)\]
\[g”(-6)=96>0\ \text{so local minimum at }x=-6\ (g(-6)=0).\]
\[g”\!\left(\frac{-3-\sqrt{57}}{4}\right)<0\ \text{so local maximum at }x=\frac{-3-\sqrt{57}}{4}\approx -2.63745.\] \[g''\!\left(\frac{-3+\sqrt{57}}{4}\right)>0\ \text{so local minimum at }x=\frac{-3+\sqrt{57}}{4}\approx 1.13745.\]
Detailed Explanation
Problem: Analyze and Solve the function \(g(x) = x(x – 2)(x + 6)^2\)
The goal is to analyze the properties of this polynomial function, including its roots, intercepts, and expansion.
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Step 1 – Identify the roots (x-intercepts):
To find the roots, we set the function equal to zero: \(x(x – 2)(x + 6)^2 = 0\).
Using the Zero Product Property, we solve for each factor separately:
- \(x = 0\)
- \(x – 2 = 0 \implies x = 2\)
- \((x + 6)^2 = 0 \implies x = -6\)
The roots are \(x = 0\), \(x = 2\), and \(x = -6\).
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Step 2 – Determine the multiplicity of each root:
The multiplicity tells us how the graph behaves at the x-axis:
- \(x = 0\) has a multiplicity of \(1\) (odd), so the graph crosses the x-axis.
- \(x = 2\) has a multiplicity of \(1\) (odd), so the graph crosses the x-axis.
- \(x = -6\) has a multiplicity of \(2\) (even), so the graph touches the x-axis and bounces back.
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Step 3 – Find the y-intercept:
To find the y-intercept, evaluate the function at \(x = 0\):
\(g(0) = 0(0 – 2)(0 + 6)^2\)
\(g(0) = 0\cdot(-2)\cdot 36 = 0\)
The y-intercept is \((0, 0)\).
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Step 4 – Expand the polynomial expression:
First, expand the squared term: \((x + 6)^2 = (x + 6)(x + 6) = x^2 + 12x + 36\).
Next, multiply the first two factors: \(x(x – 2) = x^2 – 2x\).
Now, multiply these two results together:
\((x^2 – 2x)(x^2 + 12x + 36)\)
\(= x^2(x^2 + 12x + 36) – 2x(x^2 + 12x + 36)\)
\(= x^4 + 12x^3 + 36x^2 – 2x^3 – 24x^2 – 72x\)
Combine like terms:
\(g(x) = x^4 + 10x^3 + 12x^2 – 72x\)
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Step 5 – Determine end behavior:
The leading term is \(x^4\). Since the degree (\(4\)) is even and the leading coefficient (\(1\)) is positive, the end behavior is:
As \(x \to \infty,\, g(x) \to \infty\)
As \(x \to -\infty,\, g(x) \to \infty\)
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Final Summary:
The function \(g(x) = x(x – 2)(x + 6)^2\) is a fourth-degree polynomial with roots at \(x = -6\) (touch), \(x = 0\) (cross), and \(x = 2\) (cross). In standard form, the function is written as \(g(x) = x^4 + 10x^3 + 12x^2 – 72x\).
Graph
FAQs
What is the domain of \(g(x)=x(x-2)(x+6)^2\)?
What are the zeros and their multiplicities?
What are the x- and y-intercepts?
What is the end behavior of \(g(x)\)?
How does the graph behave at each zero?
What is \(g'(x)\) and the critical points?
Where are the local maxima and minima?
On which intervals is \(g(x)\) positive or negative?
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