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JEE Main 20245 AprilMorning Shift
Exam
JEE Main
Year
2024
Date
5 April
Shift
Morning Shift
Subject
Mathematics
Chapter
Functions

JEE Main 2024 · 5 April · Morning Shift · Mathematics · Functions

Let f(x)=x^5+2 x^3+3 x+1, x ∈ R , and g(x) be a function such that...

Let f(x)=x5+2x3+3x+1,x∈Rf(x)=x^5+2 x^3+3 x+1, x \in \mathbf{R}, and g(x)g(x) be a function such that g(f(x))=xg(f(x))=x for all x∈Rx \in \mathbf{R}. Then g(7)g′(7)\frac{g(7)}{g^{\prime}(7)} is equal to :

Options

  1. A14
  2. B42
  3. C7
  4. D1

Correct answer

A. 14

Step-by-step solution

f(x)=x5+2x3+3x+1f′(x)=5x4+6x2+3f′(1)=5+6+3=14g(f(x))=xg′(f(x))f′(x)=1 for f(x)=7⇒x5+2x3+3x+1=7⇒x=1g′(7)f′(1)=1⇒g′(7)=1f′(1)=114\begin{aligned} & f(x)=x^5+2 x^3+3 x+1 \\ & f^{\prime}(x)=5 x^4+6 x^2+3 \\ & f^{\prime}(1)=5+6+3=14 \\ & g(f(x))=x \\ & g^{\prime}(f(x)) f^{\prime}(x)=1 \\ & \text{ for } f(x)=7 \\ & \Rightarrow x^5+2 x^3+3 x+1=7 \\ & \Rightarrow x=1 \\ & g^{\prime}(7) f^{\prime}(1)=1 \Rightarrow g^{\prime}(7)=\frac{1}{f^{\prime}(1)}=\frac{1}{14}\end{aligned}x=1,f(x)=7⇒g(7)=1g(7)g′(7)=11/14=14\begin{aligned} & x=1, f(x)=7 \Rightarrow g(7)=1 \\ & \frac{g(7)}{g^{\prime}(7)}=\frac{1}{1 / 14}=14\end{aligned}$
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