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14 February, 00:01

The maximum value of f (x) = x3 - 3x2 - 9x + 2 on the interval [0, 6] is

2

56

135

+5
Answers (2)
  1. 14 February, 02:14
    0
    f (x) = x^3 - 3x^2 - 9x + 2

    df/dx = 3x^2 - 6x - 9

    0 = 3 (x^2 - 2x-3)

    = 3 (x-3) (x+1)

    the maximum or minimum is at 3, - 1

    since we are in the interval from [0,6] we will use 3

    f (3) = 3^3 - 3*3^2 - 9 (3) + 2 = - 25 (this is a minimum)

    f (0) = 0-0-0+2 = 2

    f (6) = 6^3 - 3*6^2 - 9 (6) + 2 = 56 (this will be our max)
  2. 14 February, 03:43
    0
    The maximum value of f (x) in the interval [0,6] is 56

    Step-by-step explanation:

    At maximum value of f (x) we have f' (x) = 0

    That is

    f' (x) = 3x² - 6x - 9 = 0

    x² - 2x - 3 = 0

    (x - 3) (x + 1) = 0

    x = 3 or x = - 1

    Here x = 3 only lies in [0, 6].

    Let us find f'' (3) value

    f'' (x) = 6x - 6 = 6 x 3 - 6 = 12>0

    Sign of f'' (3) is positive, hence at 3 the function is minimum.

    Let us find f (0) and f (6)

    f (0) = 3 x 0³ - 3 x 0² - 9 x 0 + 2 = 2

    f (6) = 6³ - 3 x 6² - 9 x 6 + 2 = 216 - 108 - 54 + 2 = 56

    The maximum value of f (x) in the interval [0,6] is 56
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