JEE Main & Advanced Mathematics Differentiation Question Bank Differentiation by Substitution

  • question_answer
    If \[y={{\tan }^{-1}}\left( \frac{x}{1+\sqrt{1-{{x}^{2}}}} \right)\], then \[\frac{dy}{dx}=\]

    A)            \[\frac{1}{2\sqrt{1-{{x}^{2}}}}\]

    B)            \[1-\sqrt{1-{{x}^{2}}}\]

    C)            \[\frac{1}{2}\]

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

    Correct Answer: A

    Solution :

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


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