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JEE Main 202227 JulyEvening Shift
Exam
JEE Main
Year
2022
Date
27 July
Shift
Evening Shift
Subject
Mathematics
Chapter
Functions

JEE Main 2022 · 27 July · Evening Shift · Mathematics · Functions

The domain of the function f(x) = ^ - 1 [2 x ^ 2 - 3] + _ 2...

The domain of the function f(x)=sin⁡−1f\left(x\right) = \sin^{- 1}\left[2{x}^{2} - 3\right] + \log_{2}\left(log\dfrac{1}{2}\left({x}^{2} - 5x + 5\right)\right),where[t], where \left[t\right] is the greatest integer function, is

Options

  1. A(−52,5−52)\left(- \sqrt{\dfrac{5}{2}}, \dfrac{5 - \sqrt{5}}{2}\right)
  2. B(5−52,5+52)\left(\dfrac{5 - \sqrt{5}}{2}, \dfrac{5 + \sqrt{5}}{2}\right)
  3. C(1,5−52)\left(1, \dfrac{5 - \sqrt{5}}{2}\right)
  4. D[1,5+52)\left[1, \dfrac{5 + \sqrt{5}}{2}\right)

Correct answer

C. (1,5−52)\left(1, \dfrac{5 - \sqrt{5}}{2}\right)

Step-by-step solution

Given ff\left(x\right) = \sin^{- 1}[2x2−3]+log⁡2(log12(x2−5x+5))\left[2{x}^{2} - 3\right] + \log_{2}\left(log\dfrac{1}{2}\left({x}^{2} - 5x + 5\right)\right)

For f(x)f\left(x\right) to be defined

−1≤[2x2−3]<1- 1 \le \left[2{x}^{2} - 3\right] < 1

⇒−1≤2x2−3<2⇒ - 1 \le 2{x}^{2} - 3 < 2

⇒2<2x2<5⇒ 2 < 2{x}^{2} < 5

⇒1<x2<52⇒ 1 < {x}^{2} < \dfrac{5}{2}

i.e. x∈(−52,−1)∪(1,52)...(i)x \in \left(- \sqrt{\dfrac{5}{2}}, - 1\right) \cup \left(1, \sqrt{\dfrac{5}{2}}\right) . . . \left(i\right)

and x2−5x+5>0{x}^{2} - 5x + 5 > 0

⇒(x−(5−52))(x−(5+52))>0⇒ \left(x - \left(\dfrac{5 - \sqrt{5}}{2}\right)\right)\left(x - \left(\dfrac{5 + \sqrt{5}}{2}\right)\right) > 0

i.e. \left(- \infty , \dfrac{5 - \sqrt{5}}{2}\right) \cup \left(\dfrac{5 + \sqrt{5}}{2}, \infty\right) . . . \left(ii\right)</p><p>Also</p><p>Alsolog\dfrac{1}{2}\left({x}^{2} - 5x + 5\right) > 0</p><p></p><p>⇒ {x}^{2} - 5x + 5 < 1</p><p></p><p>⇒ {x}^{2} - 5x + 4 < 0</p><p>i.e.</p><p>i.e.x \in \left(1, 4\right) . . . \left(iii\right)</p><p>From(i),(ii) and (iii)</p><p>From \left(i\right), \left(ii\right) \text{ and } \left(iii\right)

So, x∈(1,5−52)x \in \left(1, \dfrac{5 - \sqrt{5}}{2}\right)

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