JAMIA MILLIA ISLAMIA Jamia Millia Islamia Solved Paper-2008

  • question_answer
        For the curve\[xy={{c}^{2}},\]the subnormal at any point varies as

    A)  \[\frac{{{x}^{2}}}{{{c}^{2}}}\]                                    

    B)  \[\frac{{{x}^{3}}}{c}\]

    C)  \[\frac{{{y}^{2}}}{{{c}^{2}}}\]                                    

    D)  \[\frac{-{{y}^{3}}}{{{c}^{2}}}\]

    Correct Answer: D

    Solution :

                    Given that,\[xy={{c}^{2}}\] \[\Rightarrow \]               \[y=\frac{{{c}^{2}}}{x}\] On differentiating w.r.t.\[x,\]we get                 \[\frac{dy}{dx}=\frac{-{{c}^{2}}}{{{x}^{2}}}\] \[\therefore \]Subnormal\[=y\frac{dy}{dx}=y\left( \frac{-{{c}^{2}}}{{{x}^{2}}} \right)\]                 \[=\frac{-y{{c}^{2}}}{{{\left( \frac{{{c}^{2}}}{y} \right)}^{2}}}=\frac{-{{y}^{3}}}{{{c}^{2}}}\]


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