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Explain solution RD Sharma class 12 chapter Maxima and Minima exercise Multiple choice question, question 27 maths

Answers (1)

Answer: option (b) -1

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

Given: f(x)=2x^3-3x^2-12x+5

Solution:

We have,

f(x)=2x^3-3x^2-12x+5                                                    

f'(x)=6x^2-6x-12                                           

For maxima and minima f'(x)=0

\begin{aligned} &\Rightarrow 6 x^{2}-6 x-12=0 \\ &\Rightarrow x^{2}-x-2=0 \\ &\Rightarrow(x-2)(x+1)=0 \\ &\Rightarrow x=2,-1 \end{aligned}

Now,

f''(x)=12x-6

f''(-1)=12(-1)-6=-12-6=-18<0

So, x = -1 is the local maxima.

f''(2)=12(2)-6=24-6=18>0

So, x = 2 is the local minima.

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