JEE Main & Advanced JEE Main Paper (Held On 8 April 2017)

  • question_answer
    The value of \[{{\tan }^{-1}}\left[ \frac{\sqrt{1+{{x}^{2}}}+\sqrt{1-{{x}^{2}}}}{\sqrt{1+{{x}^{2}}}-\sqrt{1-{{x}^{2}}}} \right],|x|<\frac{1}{2},x\ne 0,\]is equal to:          [JEE Online 08-04-2017]

    A) \[\frac{\pi }{4}+\frac{1}{2}{{\cos }^{-1}}{{x}^{2}}\]           

    B) \[\frac{\pi }{4}-{{\cos }^{-1}}{{x}^{2}}\]

    C) \[\frac{\pi }{4}-\frac{1}{2}{{\cos }^{-1}}{{x}^{2}}\]            

    D) \[\frac{\pi }{4}+{{\cos }^{-1}}{{x}^{2}}\]

    Correct Answer: A

    Solution :

                    \[{{x}^{2}}=\cos 2\theta ;\theta =\frac{1}{2}\cos {{x}^{2}}\]                 \[{{\tan }^{-1}}\left[ \frac{\sqrt{1+\cos 2\theta }+\sqrt{1-\cos 2\theta }}{\sqrt{1+\cos 2\theta }-\sqrt{1-\cos 2\theta }} \right]\]                 \[{{\tan }^{-1}}\left[ \frac{1+\tan \theta }{1-\tan \theta } \right]\]                 \[={{\tan }^{-1}}\left[ \tan \left( \frac{\pi }{4}+\theta  \right) \right]\]                 \[=\frac{\pi }{4}+\frac{1}{2}\cos {{x}^{2}}\]


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