JEE Main & Advanced Mathematics Differentiation Question Bank Differentiation by Substitution

  • question_answer
    The differential coefficient of \[{{\tan }^{-1}}\left( \frac{\sqrt{1+{{x}^{2}}}-1}{x} \right)\] with respect to \[{{\tan }^{-1}}\]x  is   [Kurukshetra CEE 1998; RPET 1999]

    A)            \[\frac{1}{2}\]

    B)            \[-\frac{1}{2}\]

    C)            1

    D)  None of these

    Correct Answer: A

    Solution :

               Let \[{{y}_{1}}={{\tan }^{-1}}\left( \frac{\sqrt{1+{{x}^{2}}}-1}{x} \right)\] and \[{{y}_{2}}={{\tan }^{-1}}x\]            Now  \[\frac{d{{y}_{1}}}{dx}=\frac{d}{dx}\left[ {{\tan }^{-1}}\tan \frac{\theta }{2} \right],\]   [By putting \[x=\tan \theta ]\]            Þ\[\frac{d{{y}_{1}}}{dx}=\frac{d}{dx}\left[ {{\tan }^{-1}}\tan \frac{\theta }{2} \right]=\frac{1}{2(1+{{x}^{2}})}\]& \[\frac{d{{y}_{2}}}{dx}=\frac{1}{1+{{x}^{2}}}\]                    Hence \[\frac{d{{y}_{1}}}{d{{y}_{2}}}=\frac{1}{2}\].


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