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NDA 2019
Exam
NDA
Year
2019
Subject
Mathematics
Chapter
Application of Derivatives

NDA 2019 · Mathematics · Application of Derivatives

Paragraph: Consider the function f(x)=3 x^4-20 x^3-12 x^2+288 x+1...

Paragraph: Consider the function f(x)=3x4−20x3−12x2+288x+1f(x)=3 x^4-20 x^3-12 x^2+288 x+1
Question: In which one of the following intervals is the function increasing?

Options

  1. A(−2,3)(-2,3)
  2. B(3,4)(3,4)
  3. C(−3,−2)(-3,-2)
  4. D(−4,−3)(-4,-3)

Correct answer

A. (−2,3)(-2,3)

Step-by-step solution

f(x)=3x4−20x3−12x2+288x+1∴f′(x)=12x3−60x2−24x+288f(x)=3 x^4-20 x^3-12 x^2+288 x+1\therefore f^{\prime}(x)=12 x^3-60 x^2-24 x+288⇒f′(x)=(x+2)(x′−3)(x−4)f′(x)>0⇒(x+2)(x−3)(x−4)>0\begin{aligned} & \Rightarrow f^{\prime}(x)=(x+2)\left(x^{\prime}-3\right)(x-4) \\ & f^{\prime}(x) > 0 \\ & \Rightarrow(x+2)(x-3)(x-4) > 0\end{aligned}$<br/><br/>\therefore \quad x \in(-2,3) \cup(4, \infty)$
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