Medium MCQ +4 / -1 PYQ · JEE Mains 2022

If the absolute maximum value of the function $$f(x)=\left(x^{2}-2 x+7\right) \mathrm{e}^{\left(4 x^{3}-12 x^{2}-180 x+31\right)}$$ in the interval $[-3,0]$ is $f(\alpha)$, then :

  1. A $\alpha=0$
  2. B $\alpha=-3$ Correct answer
  3. C $\alpha \in(-1,0)$
  4. D $\alpha \in(-3,-1]$

Solution

Given, $f(x)=\underbrace{\left(x^{2}-2 x+7\right)}_{f_{1}(x)} \underbrace{e^{\left(4 x^{3}-12 x^{2}-180 x+31\right)}}_{f_{2}(x)}$ <br/><br/> $f_{1}(x)=x^{2}-2 x+7$ <br/><br/> $f_{1}^{\prime}(x)=2 x-2$, so $f(x)$ is decreasing in $[-3,0]$ and positive also <br/><br/> $f_{2}(x)=e^{4 x^{3}-12 x^{2}-180 x+31}$ <br/><br/> $f_{2}^{\prime}(x)=e^{4 x^{3}-12 x^{2}-180 x+31} \cdot 12 x^{2}-24 x-180$ <br/><br/> $=12(x-5)(x+3) e^{4 x^{3}-12 x^{2}-180 x+31}$ <br/><br/> So, $f_{2}(x)$ is also decreasing and positive in $\{-3,0\}$ <br/><br/> $\therefore$ absolute maximum value of $f(x)$ occurs at $x=-3$ <br/><br/> $\therefore \quad \alpha=-3$

About this question

Subject: Mathematics · Chapter: Application of Derivatives · Topic: Tangents and Normals

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