JAMIA MILLIA ISLAMIA Jamia Millia Islamia Solved Paper-2010

  • question_answer
        If the normal at\[\left( ct,\frac{c}{t} \right)\]on the curve\[xy={{c}^{2}}\]meets the curve again in t, then

    A)  \[t=-\frac{1}{{{t}^{3}}}\]                             

    B)  \[t=-\frac{1}{t}\]

    C)  \[t=\frac{1}{{{t}^{2}}}\]                               

    D)  \[t{{}^{2}}=-\frac{1}{{{t}^{2}}}\]

    Correct Answer: A

    Solution :

                    The equation of normal at\[\left( ct,\frac{c}{t} \right)\]on the curve \[xy={{c}^{2}}\]is \[ty={{t}^{3}}x-c{{t}^{4}}+c\] If it passes through\[\left( ct,\frac{c}{t} \right)\]then \[t\frac{c}{t}={{t}^{3}}.ct-c{{t}^{4}}+c\] \[\Rightarrow \]               \[t={{t}^{3}}t{{}^{2}}-{{t}^{4}}t+t\] \[\Rightarrow \]               \[t-t={{t}^{3}}t(t-t)\] \[\Rightarrow \]               \[1=-{{t}^{3}}t\] \[\Rightarrow \]               \[t=-\frac{1}{{{t}^{3}}}\]


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