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

Let f : R $-$ {3} $\to$ R $-$ {1} be defined by f(x) = ${{x - 2} \over {x - 3}}$.

Let g : R $\to$ R be given as g(x) = 2x $-$ 3. Then, the sum of all the values of x for which f$-$1(x) + g$-$1(x) = ${{13} \over 2}$ is equal to :

  1. A 3
  2. B 5 Correct answer
  3. C 2
  4. D 7

Solution

Finding inverse of f(x)<br><br>$$y = {{x - 2} \over {x - 3}} \Rightarrow xy - 3y = x - 2 \Rightarrow x(y - 1) = 3y - 2$$<br><br>$\therefore$ ${f^{ - 1}}(x) = {{3x - 2} \over {x - 1}}$<br><br>Similarly for ${g^{ - 1}}(x)$<br><br>$$y = 2x - 3 \Rightarrow x = {{y + 3} \over 2} \Rightarrow {g^{ - 1}}(x) = {{x + 3} \over 2}$$<br><br>$\therefore$ ${{3x - 2} \over {x - 1}} + {{x + 3} \over 2} = {{13} \over 2}$<br><br>$\Rightarrow 6x - 4 + {x^2} + 2x - 3 = 13x - 13$<br><br>$\Rightarrow {x^2} - 5x + 6 = 0$<br><br>$\Rightarrow (x - 2)(x - 3) = 0$<br><br>$\Rightarrow$ x = 2 or 3

About this question

Subject: Mathematics · Chapter: Sets, Relations and Functions · Topic: Sets and Operations

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