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Need solution for RD Sharma maths class 12 chapter Maxima and Minima exercise Multiple Choice question, question 17.

Answers (1)

Answer: least=0,  greatest=54

Hint: For local maxima or minima, we must have f'(x)=0.

Given: f(x)=x^3-6x^2+9x

Solution:

We have,

f(x)=x^3-6x^2+9x

\Rightarrow f'(x)=3x^2-12x+9                                         

For maxima and minima f'(x)=0

\Rightarrow 3x^2-12x+9=0

\Rightarrow x^2-4x+3=0

\Rightarrow (x-1)(x-3)=0

\Rightarrow x=1,3

Now,

f(1)=1^3-6(1)^2+9(1)=1-6+9=4

f(3)=3^3-6(2)^2+9(6)=27-54+27=0

And at the extreme point of [0, 6]

f(0)=0^3-6(0)^2+9(0)=0

f(6)=6^3-6(6)^2+9(6)=216-216+54=54

The least and greatest values of f(x)=x^3-6x^2+9x  in (0 ,6) are 0 and 54.

Note: Option is not matching with the answer, given in the book.

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infoexpert24

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