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.

  1. 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 \(x = -6\).

  2. 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.
  3. 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 \((0, 0)\).

  4. 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:

    \(g(x) = x^4 + 10x^3 + 12x^2 – 72x\)

  5. 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 \(x \to -\infty,\, g(x) \to \infty\)

  6. 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 \(g(x) = x^4 + 10x^3 + 12x^2 – 72x\).

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FAQs

What is the domain of \(g(x)=x(x-2)(x+6)^2\)?

The domain is all real numbers: \((-\infty,\infty)\). Polynomial functions are defined everywhere.

What are the zeros and their multiplicities?

Zeros: \(x=0\) (multiplicity 1), \(x=2\) (multiplicity 1), \(x=-6\) (multiplicity 2).

What are the x- and y-intercepts?

x-intercepts: \((0,0)\), \((2,0)\), \((-6,0)\). y-intercept: \(g(0)=0\) (same as one x-intercept).

What is the end behavior of \(g(x)\)?

Degree is 4 with leading coefficient 1, so leading term \(x^4\). Thus \(g(x)\to+\infty\) as \(x\to\pm\infty\).

How does the graph behave at each zero?

At \(x=-6\) (even multiplicity 2) the graph touches and bounces. At \(x=0\) and \(x=2\) (odd multiplicity 1) it crosses the x-axis.

What is \(g'(x)\) and the critical points?

What is \(g'(x)\) and the critical points?

Where are the local maxima and minima?

Using sign changes: local minimum at \(x=-6\); local maximum at \(x\approx-2.637\); local minimum at \(x\approx1.137\). Evaluate \(g\) there for y-values.

On which intervals is \(g(x)\) positive or negative?

Sign determined by factors \(x\), \(x-2\), and \((x+6)^2\) (always nonnegative). So sign equals sign of \(x(x-2)\): positive for \(x < 0\) and \(x > 2\); negative for \(0 < x < 2\). Note multiplicity at -6 does not change sign.
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