JEE Main & Advanced Mathematics Differentiation Question Bank Differentiation by Substitution

  • question_answer
    If \[y={{\sin }^{-1}}\sqrt{1-{{x}^{2}}}\], then \[dy/dx=\]                 [AISSE 1987]

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

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

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

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

    Correct Answer: C

    Solution :

               \[y={{\sin }^{-1}}(\sqrt{1-{{x}^{2}}})\]            Let \[\sqrt{1-{{x}^{2}}}=\sin \theta \Rightarrow 1-{{x}^{2}}={{\sin }^{2}}\theta \]            Þ  \[{{x}^{2}}=1-{{\sin }^{2}}\theta ={{\cos }^{2}}\theta \]            \[\therefore x=\cos \theta \] or \[\theta ={{\cos }^{-1}}x\] \[\Rightarrow y={{\cos }^{-1}}x\]            Differentiating w.r.t. x of y, we get  \[\frac{dy}{dx}=-\frac{1}{\sqrt{1-{{x}^{2}}}}\].


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