RAJASTHAN ­ PET Rajasthan PET Solved Paper-2007

  • question_answer
    Let\[f:(-1,1)\to B\]is defined as \[f(x)={{\tan }^{-1}}\frac{2x}{1-{{x}^{2}}}.\]Function\[f\]is one-one and onto, then the interval B is

    A)  \[\left( 0,\frac{\pi }{2} \right)\]

    B)  \[\left[ 0,\frac{\pi }{2} \right)\]

    C)  \[\left[ -\frac{\pi }{2},\frac{\pi }{2} \right]\]

    D)  \[\left( -\frac{\pi }{2},\frac{\pi }{2} \right)\]

    Correct Answer: D

    Solution :

     \[x\in (-1,1)\Rightarrow {{\tan }^{-1}}x\in \left( -\frac{\pi }{4},\frac{\pi }{4} \right)\] \[\Rightarrow \] \[2{{\tan }^{-1}}x\in \left( -\frac{\pi }{2},\frac{\pi }{2} \right)\] and \[f(x)={{\tan }^{-1}}\frac{2x}{1-{{x}^{2}}}=2{{\tan }^{-1}}x,({{x}^{2}}<1)\] \[\therefore \] \[f(x)\in \left( -\frac{\pi }{2},\frac{\pi }{2} \right)\] Function is one-one onto.


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