JEE Main & Advanced Mathematics Differentiation Question Bank Differentiation by Substitution

  • question_answer
    If \[y={{\tan }^{-1}}\left( \frac{x}{\sqrt{1-{{x}^{2}}}} \right)\], then \[\frac{dy}{dx}=\]      [MP PET 1999]

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

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

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

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

    Correct Answer: C

    Solution :

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


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