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Need solution for RD Sharma maths class 12 chapter Maxima and Minima exercise Multiple Choice question, question 21.

Answers (1)

Answer: option(d) None of these

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

Given: f(x)=x+\frac{1}{x}

Solution:

We have,

f(x)=x+\frac{1}{x}                                              

f'(x)=1-\frac{1}{x^2}                       

For maxima and minima f'(x)=0

\Rightarrow 1-\frac{1}{x^2}=0

\Rightarrow x^2-1=0

\Rightarrow x^2=1

\Rightarrow x=\pm 1

\Rightarrow x= 1(x>0)

Now,

f''(x)=\frac{2}{x^3}

f''(1)=\frac{2}{1^3}=2>0

So, x = 1 is a local minima.

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infoexpert24

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