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Provide solution for RD Sharma maths class12 Chapter Maxima and Minima exercise Multiple choice question, question 10.

Answers (1)

Answer: option(c) 3   

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

Given: f(x)=\sum_{r-1}^{5}(x-r)^2

Solution:

We have,

f(x)=\sum_{r-1}^{5}(x-r)^2

\begin{aligned} &f(x)=(x-1)^{2}+(x-2)^{2}+(x-3)^{2}+(x-4)^{2}+(x-5)^{2} \\ &f^{\prime}(x)=2(x-1+x-2+x-3+x-4+x-5) \\ &f^{\prime}(x)=2(5 x-15) \end{aligned}

For maxima and minima

f'(x)=0

\Rightarrow 2(5x-15)=0

\Rightarrow 5x-15=0

\Rightarrow 5x=15

\Rightarrow x=3

Now,

f''(x)=10>0

So, x =3  is a point of local minima.

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infoexpert24

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