JEE Main & Advanced Mathematics Differentiation Question Bank Derivative at a point Standard Differentiation

  • question_answer
    If \[y={{\sin }^{-1}}(x\sqrt{1-x}+\sqrt{x}\sqrt{1-{{x}^{2}})},\]then \[\frac{dy}{dx}=\] [Roorkee 1981; MP PET 2004]

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

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

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

    D)            None of these

    Correct Answer: C

    Solution :

               Putting \[x=\sin A\] and \[\sqrt{x}=\sin B\]            \[y={{\sin }^{-1}}(\sin A\sqrt{1-{{\sin }^{2}}B}+\sin B\sqrt{1-{{\sin }^{2}}A})\]              \[={{\sin }^{-1}}[\sin (A+B)]=A+B={{\sin }^{-1}}x+{{\sin }^{-1}}\sqrt{x}\]            Þ \[\frac{dy}{dx}=\frac{1}{\sqrt{1-{{x}^{2}}}}+\frac{1}{2\sqrt{x-{{x}^{2}}}}\].


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