JEE Main & Advanced Mathematics Applications of Derivatives Question Bank Application in Mechanics and Rate Measurer

  • question_answer
    The rate of change of \[\sqrt{({{x}^{2}}+16)}\] with respect to \[\frac{x}{x-1}\] at \[x=3\] is [AMU 2001; MP PET 1987]

    A)            2

    B)            \[\frac{11}{5}\]

    C)            \[-\frac{12}{5}\]

    D)            \[-3\]

    Correct Answer: C

    Solution :

               Let \[y=\sqrt{{{x}^{2}}+16}\] and \[z=\frac{x}{x-1}\]                    Þ\[\frac{dy}{dx}=\frac{1}{2}{{({{x}^{2}}+16)}^{-1/2}}(2x)\]&\[\frac{dz}{dx}=\frac{x-1-x}{{{(x-1)}^{2}}}=\frac{-1}{{{(x-1)}^{2}}}\]                    \ \[\frac{dy}{dz}=\frac{-x}{\sqrt{{{x}^{2}}+16}}\,\frac{1}{1/{{(x-1)}^{2}}}\]                      \[{{\left( \frac{dy}{dz} \right)}_{x=3}}=\frac{-3{{(2)}^{2}}}{5}=\frac{-12}{5}\].


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