JEE Main & Advanced Mathematics Differentiation Question Bank Differentiation by Substitution

  • question_answer
    If \[y={{\sin }^{-1}}\left( \frac{1-{{x}^{2}}}{1+{{x}^{2}}} \right)\], then \[\frac{dy}{dx}\] equals [EAMCET 1991; RPET 1996]

    A)   \[\frac{2}{1-{{x}^{2}}}\]

    B)   \[\frac{1}{1+{{x}^{2}}}\]

    C)            \[\pm \frac{2}{1+{{x}^{2}}}\]

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

    Correct Answer: C

    Solution :

               \[y={{\sin }^{-1}}\left( \frac{1-{{x}^{2}}}{1+{{x}^{2}}} \right)\]            Put \[x=\tan \theta \]Þ \[\theta ={{\tan }^{-1}}x\]            \[\therefore y={{\sin }^{-1}}\cos 2\theta =\frac{\pi }{2}\pm 2\theta \]            \[y=\frac{\pi }{2}\pm 2{{\tan }^{-1}}x\]\[\Rightarrow \]\[\frac{dy}{dx}=\frac{\pm 2}{1+{{x}^{2}}}\].


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