JEE Main & Advanced Sample Paper JEE Main Sample Paper-47

  • question_answer
    If \[{{({{\tan }^{-1}}x)}^{2}}+{{({{\cot }^{-1}})}^{2}}=\frac{5{{\pi }^{2}}}{8},\] then \[x\] is equal to

    A)  0                                

    B)  - 1

    C)  - 2                              

    D)  - 3

    Correct Answer: B

    Solution :

     \[{{({{\tan }^{-1}}x)}^{2}}+{{\left( \frac{\pi }{2}-{{\tan }^{-1}} \right)}^{2}}=\frac{5{{\pi }^{2}}}{8}\] \[\Rightarrow \]            \[2\,{{({{\tan }^{-1}}x)}^{2}}-\pi \,({{\tan }^{-1}}x)-\frac{3{{\pi }^{2}}}{8}=0\] \[\therefore \]    \[{{\tan }^{-1}}x=\frac{\pi \pm \,\sqrt{4{{\pi }^{2}}}}{4}\]\[=\frac{\pi \pm 2\pi }{4}\] \[\Rightarrow \]            \[{{\tan }^{-1}}x=\frac{3\pi }{4}\] or \[-\frac{\pi }{4}\] \[\therefore \]    \[x=-1\] for \[-1\] \[\Rightarrow \]            \[x=-1\]


You need to login to perform this action.
You will be redirected in 3 sec spinner