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Find the 
x-coordinates of all relative minima of 
f(x).

f(x)=-3x^(3)-36x^(2)+81 x-46
Answer: 
x=

Find the x x -coordinates of all relative minima of f(x) f(x) .\newlinef(x)=3x336x2+81x46 f(x)=-3 x^{3}-36 x^{2}+81 x-46 \newlineAnswer: x= x=

Full solution

Q. Find the x x -coordinates of all relative minima of f(x) f(x) .\newlinef(x)=3x336x2+81x46 f(x)=-3 x^{3}-36 x^{2}+81 x-46 \newlineAnswer: x= x=
  1. Find Critical Points: To find the relative minima of the function f(x)f(x), we need to find the critical points by taking the derivative of f(x)f(x) and setting it equal to zero.\newlinef(x)=3x336x2+81x46f(x) = -3x^3 - 36x^2 + 81x - 46\newlineLet's find the first derivative f(x)f'(x).\newlinef(x)=ddx(3x336x2+81x46)f'(x) = \frac{d}{dx} (-3x^3 - 36x^2 + 81x - 46)\newlinef(x)=9x272x+81f'(x) = -9x^2 - 72x + 81
  2. Solve Quadratic Equation: Now, we need to find the values of xx for which f(x)=0f'(x) = 0.9x272x+81=0-9x^2 - 72x + 81 = 0To solve this quadratic equation, we can factor it or use the quadratic formula. Let's try to factor it first.9(x2+8x9)=0-9(x^2 + 8x - 9) = 0Now, we look for two numbers that multiply to 9-9 and add up to 88. The numbers are 99 and 1-1.9(x+9)(x1)=0-9(x + 9)(x - 1) = 0
  3. Identify Critical Points: We have two potential critical points from the factored equation:\newlinex+9=0x + 9 = 0 or x1=0x - 1 = 0\newlineSolving these, we get:\newlinex=9x = -9 or x=1x = 1\newlineThese are the critical points where the derivative is zero, but we need to determine which of these points are relative minima.
  4. Second Derivative Test: To determine if these critical points are relative minima, we can use the second derivative test. Let's find the second derivative f(x)f''(x). \newlinef(x)=ddx(9x272x+81)f''(x) = \frac{d}{dx} (-9x^2 - 72x + 81)\newlinef(x)=18x72f''(x) = -18x - 72
  5. Evaluate at x=9x = -9: Now, we evaluate the second derivative at the critical points.\newlineFor x=9x = -9:\newlinef(9)=18(9)72f''(-9) = -18(-9) - 72\newlinef(9)=16272f''(-9) = 162 - 72\newlinef(9)=90f''(-9) = 90\newlineSince f''(-9) > 0, the function is concave up at x=9x = -9, indicating a relative minimum.
  6. Evaluate at x=1x = 1: For x=1x = 1:
    f(1)=18(1)72f''(1) = -18(1) - 72
    f(1)=1872f''(1) = -18 - 72
    f(1)=90f''(1) = -90
    Since f''(1) < 0, the function is concave down at x=1x = 1, indicating a relative maximum, not a minimum.

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