Questions: Complete parts (a) through (c) for the following function. f(x)=-3x^3+6x^2-4x-4 (a) Find intervals where the function is increasing or decreasing, and determine any relative extrema. (b) Find intervals where the function is concave upward or concave downward, and determine any inflection points. (c) Graph the function, considering the domain, critical points, symmetry, relative extrema, regions where the function is increasing or decreasing, inflection points, regions where the function is concave upward or concave downward, intercepts where possible, and asymptotes where applicable.

Complete parts (a) through (c) for the following function.
f(x)=-3x^3+6x^2-4x-4
(a) Find intervals where the function is increasing or decreasing, and determine any relative extrema.
(b) Find intervals where the function is concave upward or concave downward, and determine any inflection points.
(c) Graph the function, considering the domain, critical points, symmetry, relative extrema, regions where the function is increasing or decreasing, inflection points, regions where the function is concave upward or concave downward, intercepts where possible, and asymptotes where applicable.
Transcript text: Complete parts (a) through (c) for the following function. \[ f(x)=-3 x^{3}+6 x^{2}-4 x-4 \] (a) Find intervals where the function is increasing or decreasing, and determine any relative extrema. (b) Find intervals where the function is concave upward or concave downward, and determine any inflection points. (c) Graph the function, considering the domain, critical points, symmetry, relative extrema, regions where the function is increasing or decreasing, inflection points, regions where the function is concave upward or concave downward, intercepts where possible, and asymptotes where applicable.
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Solution

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Solution Steps

Step 1: Find the First Derivative

To determine where the function is increasing or decreasing, we first find the first derivative of the function \( f(x) = -3x^3 + 6x^2 - 4x - 4 \).

\[ f'(x) = \frac{d}{dx}(-3x^3 + 6x^2 - 4x - 4) = -9x^2 + 12x - 4 \]

Step 2: Find Critical Points

Set the first derivative equal to zero to find the critical points.

\[ -9x^2 + 12x - 4 = 0 \]

Using the quadratic formula \( x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a} \), where \( a = -9 \), \( b = 12 \), and \( c = -4 \):

\[ x = \frac{-12 \pm \sqrt{12^2 - 4(-9)(-4)}}{2(-9)} = \frac{-12 \pm \sqrt{144 - 144}}{-18} = \frac{-12 \pm 0}{-18} = \frac{-12}{-18} = \frac{2}{3} \]

Step 3: Determine Intervals of Increase and Decrease

Test intervals around the critical point \( x = \frac{2}{3} \) to determine where the function is increasing or decreasing.

  • For \( x < \frac{2}{3} \), choose \( x = 0 \): \[ f'(0) = -9(0)^2 + 12(0) - 4 = -4 \quad (\text{negative, so } f(x) \text{ is decreasing}) \]

  • For \( x > \frac{2}{3} \), choose \( x = 1 \): \[ f'(1) = -9(1)^2 + 12(1) - 4 = -9 + 12 - 4 = -1 \quad (\text{negative, so } f(x) \text{ is decreasing}) \]

Final Answer

The function is decreasing on \((-\infty, \infty)\) and increasing nowhere.

Step 4: Find the Second Derivative

To determine concavity, find the second derivative of the function.

\[ f''(x) = \frac{d}{dx}(-9x^2 + 12x - 4) = -18x + 12 \]

Step 5: Find Inflection Points

Set the second derivative equal to zero to find potential inflection points.

\[ -18x + 12 = 0 \implies x = \frac{12}{18} = \frac{2}{3} \]

Step 6: Determine Intervals of Concavity

Test intervals around the potential inflection point \( x = \frac{2}{3} \).

  • For \( x < \frac{2}{3} \), choose \( x = 0 \): \[ f''(0) = -18(0) + 12 = 12 \quad (\text{positive, so } f(x) \text{ is concave upward}) \]

  • For \( x > \frac{2}{3} \), choose \( x = 1 \): \[ f''(1) = -18(1) + 12 = -6 \quad (\text{negative, so } f(x) \text{ is concave downward}) \]

Final Answer

The function is concave upward on \((-\infty, \frac{2}{3})\) and concave downward on \((\frac{2}{3}, \infty)\). There is an inflection point at \( x = \frac{2}{3} \).

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