J & K CET Engineering J and K - CET Engineering Solved Paper-2014

  • question_answer
    . Solve for \[x,\,\,{{\tan }^{-1}}(1/x)=\pi +{{\tan }^{-1}}x,\,\,0<x<1\]

    A)  not defined        

    B)  \[\sqrt{3}\]

    C)  \[\pm \,1\]                

    D)  \[0\]

    E)  None of these

    Correct Answer: E

    Solution :

    We have, \[{{\tan }^{-1}}\left( \frac{1}{x} \right)=\pi +{{\tan }^{-1}}x,\,0<x<1\] \[\Rightarrow \] \[{{\tan }^{-1}}\left( \frac{1}{x} \right)-{{\tan }^{-1}}x=\pi \] \[\Rightarrow \] \[{{\tan }^{-1}}\left( \frac{\frac{1}{x}-x}{1+\frac{1}{x}.x} \right)=\pi \] \[\Rightarrow \] \[{{\tan }^{-1}}\left( \frac{1-{{x}^{2}}}{x(1+1)} \right)=\pi \] \[\Rightarrow \] \[\frac{1-{{x}^{2}}}{2x}=\tan \pi \] \[\Rightarrow \] \[\frac{1-{{x}^{2}}}{2x}=0\] \[\Rightarrow \] \[1-{{x}^{2}}=0\,\Rightarrow {{x}^{2}}=1\,\Rightarrow x=\pm 1\] but given,  \[0<x<1\]


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