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Consider the function \newlinef(x)=x39x221x2.f(x)=x^{3}-9x^{2}-21 x-2.\newlineIts derivative is \newlinef(x)=3x218x21.f^{\prime}(x)=3x^{2}-18 x-21. help (formulas)\newlineits second derivative is \newlinef(x)=6x18f^{\prime\prime}(x)=6x-18\newlineThe graph that correctly displays \newlinef(z)f(z) (in black) and \newlinef(x)f^{\prime\prime}(x) (in orange) is\newlineA\newlineB\newlinec\newline00.\newlineB.\newlineUsing the graphs of \newlineff and \newlineff^{\prime\prime}, indicate where \newlineff is concave up and concave down. Enter DNE if such an interval does not exist: \newlineff is concave up on \newline◻ help (intervals).\newlineff is concave down on

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Q. Consider the function \newlinef(x)=x39x221x2.f(x)=x^{3}-9x^{2}-21 x-2.\newlineIts derivative is \newlinef(x)=3x218x21.f^{\prime}(x)=3x^{2}-18 x-21. help (formulas)\newlineits second derivative is \newlinef(x)=6x18f^{\prime\prime}(x)=6x-18\newlineThe graph that correctly displays \newlinef(z)f(z) (in black) and \newlinef(x)f^{\prime\prime}(x) (in orange) is\newlineA\newlineB\newlinec\newline00.\newlineB.\newlineUsing the graphs of \newlineff and \newlineff^{\prime\prime}, indicate where \newlineff is concave up and concave down. Enter DNE if such an interval does not exist: \newlineff is concave up on \newline◻ help (intervals).\newlineff is concave down on
  1. Identify Second Derivative: Identify the second derivative of the function f(x)f(x). The second derivative of the function f(x)f(x) is given as f(x)=6x18f''(x) = 6x - 18.
  2. Find Critical Points: Find the critical points of the second derivative.\newlineTo find the intervals of concavity, we need to determine where the second derivative changes sign. This occurs at the critical points of the second derivative. Set f(x)=0f''(x) = 0 and solve for xx:\newline6x18=06x - 18 = 0\newline6x=186x = 18\newline$x = \(3\)
  3. Test Intervals for Concavity: Test the intervals around the critical point to determine concavity.\(\newline\)We have one critical point, \(x = 3\). We will test the intervals \((-\infty, 3)\) and \((3, \infty)\) to see where the second derivative is positive (indicating concave up) and where it is negative (indicating concave down).\(\newline\)Choose a test point \(x = 2\) for the interval \((-\infty, 3)\):\(\newline\)\(f''(2) = 6(2) - 18 = 12 - 18 = -6\)\(\newline\)Since \(f''(2) < 0\), the function is concave down on the interval \((-\infty, 3)\).\(\newline\)Choose a test point \(x = 4\) for the interval \((3, \infty)\):\(\newline\)\((-\infty, 3)\)\(0\)\(\newline\)Since \((-\infty, 3)\)\(1\), the function is concave up on the interval \((3, \infty)\).

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