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JEE Main 202325 JanuaryMorning Shift
Exam
JEE Main
Year
2023
Date
25 January
Shift
Morning Shift
Subject
Mathematics
Chapter
Functions

JEE Main 2023 · 25 January · Morning Shift · Mathematics · Functions

Let f: (0, 1) → ℝ be a function defined by f(x) = 1 1 - e ^ - x ,...

Let f:(0,1)→Rf: \left(0, 1\right) \to \mathbb{R} be a function defined by f(x)=11−e−xf\left(x\right) = \dfrac{1}{1 - {e}^{- x}}, and g(x)=(f(−x)−f(x))g\left(x\right) = \left(f\left(- x\right) - f\left(x\right)\right). Consider two statements

(I) gg is an increasing function in \left(0, 1\right)</p><p>(II)</p><p>(II)gisone−onein(0,1)is one-one in \left(0, 1\right)
Then,

Options

  1. AOnly (I) is true
  2. BOnly (II) is true
  3. CNeither (I) nor (II) is true
  4. DBoth (I) and (II) are true

Correct answer

D. Both (I) and (II) are true

Step-by-step solution

Given,

f:(0,1)→Rbeafunctiondefinedbyf: \left(0, 1\right) \to \mathbb{R} be a function defined byf\left(x\right) = \dfrac{1}{1 - {e}^{- x}},and, andg\left(x\right) = \left(f\left(- x\right) - f\left(x\right)\right)</p><p>Nowusing</p><p>Now usingg\left(x\right) = f\left(- x\right) - f\left(x\right)weget,</p><p>we get,</p><p>g ( x ) = \dfrac{1}{1 - {e}^{x}} - \dfrac{{e}^{x}}{{e}^{x} - 1}</p><p></p><p>⇒ g\left(x\right) = \dfrac{1 + {e}^{x}}{1 - {e}^{x}}</p><p>Nowdifferentiatingtheabovefunctionwithrespectto</p><p>Now differentiating the above function with respect toxweget,</p><p>we get,</p><p>⇒ {g}^{'}\left(x\right) = \dfrac{2{e}^{x}}{{\left(1 - {e}^{x}\right)}^{2}} > 0

Since g′(x){g}^{'}\left(x\right) is always positive

So,g(x)g\left(x\right) is one-one in \left(0, 1\right)</p><p>And</p><p>Andg\left(x\right)isincreasingin(0,1)is increasing in \left(0, 1\right)

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