JEE Main & Advanced Mathematics Applications of Derivatives Question Bank Tangent and Normal

  • question_answer
    At what point on the curve \[{{x}^{3}}-8{{a}^{2}}y=0\], the slope of the normal is \[\frac{-2}{3}\] [RPET 2002]

    A)            \[(a,\,a)\]

    B)            \[(2a,\,-a)\]

    C)            \[(2a,\,a)\]

    D)            None of these

    Correct Answer: C

    Solution :

               \[{{x}^{3}}-8{{a}^{2}}y=0\]  Þ  \[3{{x}^{2}}-8{{a}^{2}}\,.\,\frac{dy}{dx}=0\]            Þ  \[3{{x}^{2}}=8{{a}^{2}}\,.\,\frac{dy}{dx}\]  Þ \[\frac{dy}{dx}=\frac{3{{x}^{2}}}{8{{a}^{2}}}\]            \ Slope of the normal = \[-\frac{1}{\left( \frac{dy}{dx} \right)}\] = \[-\frac{1}{\frac{3{{x}^{2}}}{8{{a}^{2}}}}\]\[=-\frac{8{{a}^{2}}}{3{{x}^{2}}}\]            Given \[\frac{-8{{a}^{2}}}{3{{x}^{2}}}=\frac{-2}{3}\]  \\[(x,\,y)=(2a,\,a)\].


You need to login to perform this action.
You will be redirected in 3 sec spinner