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Need solution for RD Sharma maths class 12 chapter Maxima and Minima exercise Multiple Choice question, question 16.

Answers (1)

Answer: option(b) 16

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

Given: x + y = 8

Solution:

We have,

x+y =8\Rightarrow y=8-x                                                                  …(i)

Let f(x)=xy

\Rightarrow f(x)=x(8-x)                                                         (From Equation i)

\Rightarrow f'(x)=8-2x                                             

For maxima and minima f'(x)=0

\Rightarrow 8-2x=0

\Rightarrow 8=2x

\Rightarrow x=4

\Rightarrow y=8-x=8-4=4

Now,

f''(x)=-2

f''(4)=-2<0

So, x = 4 is the local maxima.

Hence, f(4)=4 \times 4=16

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