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JEE Advanced 2008Paper 1
Exam
JEE Advanced
Year
2008
Paper
Paper 1
Subject
Mathematics
Chapter
Application of Derivatives

JEE Advanced 2008 · Paper 1 · Mathematics · Application of Derivatives

The total number of local maxima and local minima of the function...

The total number of local maxima and local minima of the function f(x)=\left\{(2+x)3;−3<x≤−1x23;−1<x<2\begin{array}{lc}(2+x)^3 ; & -3 < x \leq-1 \\ x^{\frac{2}{3}} ; & -1 < x < 2\end{array}\right. isThe total number of local maxima and local minima of the function f(x)=\ array lc (2+x)^3 ; & -3 < x ≤-1 x^ (2)/(3) ; &

Options

  1. A0
  2. B1
  3. C2
  4. D3

Correct answer

C. 2

Step-by-step solution

Given that, f(x)=\left\{(2+x)3;−3<x≤−1x2/3;−1<x<2\begin{array}{l}(2+x)^3 ;-3 < x \leq-1 \\ x^{2 / 3} ; \quad-1 < x < 2\end{array}\right. \Rightarrow \quad f^{\prime}(x)=\left\{\begin{array}{l} 3(2+x)^2 ;-3 < x \leq 1 \\ \frac{2}{3} x^{-\frac{1}{3}} ; \quad-1 < x < 2 \end{array}\right.The total number of local maxima and local minima of the function f(x)=\ array lc (2+x)^3 ; & -3 < x ≤-1 x^ (2)/(3) ; &
Clearly, f′(x)f^{\prime}(x) changes its sign at x=−1x=-1 from ++ ve to -ve and so f(x)f(x) has local maxima at x=−1x=-1. Also, f′(0)f^{\prime}(0) does not exist but f′(0−)<0f^{\prime}\left(0^{-}\right) < 0 and f′(0+)<0f^{\prime}\left(0^{+}\right) < 0. It can only be inferred that f(x)f(x) has a possibility of a minima at x=0x=0. Hence, the given function has one local maxima at x=−1x=-1 and one local minima at x=0x=0.
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