Medium MCQ +4 / -1 PYQ · JEE Mains 2021

If the domain of the function $$f(x) = {{{{\cos }^{ - 1}}\sqrt {{x^2} - x + 1} } \over {\sqrt {{{\sin }^{ - 1}}\left( {{{2x - 1} \over 2}} \right)} }}$$ is the interval ($\alpha$, $\beta$], then $\alpha$ + $\beta$ is equal to :

  1. A ${3 \over 2}$ Correct answer
  2. B 2
  3. C ${1 \over 2}$
  4. D 1

Solution

$O \le {x^2} - x + 1 \le 1$<br><br>$\Rightarrow {x^2} - x \le 0$<br><br>$\Rightarrow x \in [0,1]$<br><br>Also, $0 &lt; {\sin ^{ - 1}}\left( {{{2x - 1} \over 2}} \right) \le {\pi \over 2}$<br><br>$\Rightarrow 0 &lt; {{2x - 1} \over 2} \le 1$<br><br>$\Rightarrow 0 &lt; 2x - 1 \le 2$<br><br>$1 &lt; 2x \le 3$<br><br>${1 \over 2} &lt; x \le {3 \over 2}$<br><br>Taking intersection <br><br>$x \in \left( {{1 \over 2},1} \right]$<br><br>$\Rightarrow \alpha = {1 \over 2},\beta = 1$<br><br>$\Rightarrow \alpha + \beta = {3 \over 2}$

About this question

Subject: Mathematics · Chapter: Inverse Trigonometric Functions · Topic: Domain and Range

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