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

  • question_answer
    If \[x=y\sqrt{1-{{y}^{2}},}\]then \[\frac{dy}{dx}=\]                                                    [MP PET 2001]

    A)            0

    B)            x

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

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

    Correct Answer: C

    Solution :

               \[x=y\sqrt{1-{{y}^{2}}}\]            Differentiate with respect to x,            \[1=\frac{dy}{dx}\sqrt{1-{{y}^{2}}}+y.\frac{1}{2\sqrt{1-{{y}^{2}}}}\,.\,(-2y)\,.\,\frac{dy}{dx}\]            Þ  \[1=\frac{dy}{dx}\sqrt{1-{{y}^{2}}}-\frac{{{y}^{2}}}{\sqrt{1-{{y}^{2}}}}\,.\,\frac{dy}{dx}\]            Þ  \[1=\frac{dy}{dx}\left[ \frac{1-{{y}^{2}}-{{y}^{2}}}{\sqrt{1-{{y}^{2}}}} \right]\]Þ  \[1=\frac{dy}{dx}\left[ \frac{1-2{{y}^{2}}}{\sqrt{1-{{y}^{2}}}} \right]\]            \[\frac{dy}{dx}=\frac{\sqrt{1-{{y}^{2}}}}{1-2{{y}^{2}}}\].


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