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Let f(x)=x3−6x2+9x−8f(x) = x^3 - 6x^2 + 9x - 8 be a function, then which of the following statements are TRUE?

(A) f′(x)=3(x−1)(x−3)f'(x) = 3(x - 1)(x - 3)

(B) The critical points of the function are x=1x = 1 and x=3x = 3

(C) x=1x = 1 is the point of local minimum

(D) The local maximum value is −4-4

Choose the correct answer from the options given below:

Solution

✅ Correct Option: 2

Given: f(x)=x3−6x2+9x−8f(x) = x^3 - 6x^2 + 9x - 8

The first derivative is:

f′(x)=3x2−12x+9f'(x) = 3x^2 - 12x + 9

f′(x)=3(x2−4x+3)f'(x) = 3(x^2 - 4x + 3)

f′(x)=3(x−1)(x−3)f'(x) = 3(x - 1)(x - 3)

Statement (A) is TRUE.


For critical points, set f′(x)=0f'(x) = 0:

3(x−1)(x−3)=03(x - 1)(x - 3) = 0

(x−1)(x−3)=0(x - 1)(x - 3) = 0

The critical points are x=1x = 1 and x=3x = 3.

Statement (B) is TRUE.


The second derivative is:

f′′(x)=6x−12f''(x) = 6x - 12

At x=1x = 1:

f′′(1)=6(1)−12f''(1) = 6(1) - 12

f′′(1)=−6f''(1) = -6

Since f′′(1)<0f''(1) < 0, the point x=1x = 1 is a local maximum.

Statement (C) is FALSE.


The local maximum value at x=1x = 1:

f(1)=(1)3−6(1)2+9(1)−8f(1) = (1)^3 - 6(1)^2 + 9(1) - 8

f(1)=1−6+9−8f(1) = 1 - 6 + 9 - 8

f(1)=−4f(1) = -4

Statement (D) is TRUE.


The true statements are (A), (B), and (D).

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