CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2001

  • question_answer
    If\[3{{\sin }^{-1}}\left( \frac{2x}{1+{{x}^{2}}} \right)-4{{\cos }^{-1}}\left( \frac{1-{{x}^{2}}}{1+{{x}^{2}}} \right)\]\[+2{{\tan }^{-1}}\left( \frac{2x}{1-{{x}^{2}}} \right)=\frac{\pi }{3},\]then\[x\]is equal to:

    A)  \[\frac{1}{\sqrt{3}}\]                                    

    B)  \[-\frac{1}{\sqrt{3}}\]

    C)  \[\sqrt{3}\]                       

    D)         \[-\frac{\sqrt{3}}{2}\]

    E)  \[\frac{\sqrt{3}}{2}\]

    Correct Answer: A

    Solution :

    We have, \[3{{\sin }^{-1}}\left( \frac{2x}{1+{{x}^{2}}} \right)-4{{\cos }^{-1}}\left( \frac{1-{{x}^{2}}}{1+{{x}^{2}}} \right)\] \[+2{{\tan }^{-1}}\left( \frac{2x}{1-{{x}^{2}}} \right)=\frac{\pi }{3}\] \[\Rightarrow \]\[6{{\tan }^{-1}}x-8{{\tan }^{-1}}x+4{{\tan }^{-1}}x=\frac{\pi }{3}\] \[\Rightarrow \]                               \[2{{\tan }^{-1}}x=\frac{\pi }{3}\] \[\Rightarrow \]                               \[{{\tan }^{-1}}x=\frac{\pi }{6}\] \[\Rightarrow \]                               \[x=\tan \frac{\pi }{6}=\frac{1}{\sqrt{3}}\]


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