JCECE Engineering JCECE Engineering Solved Paper-2011

  • question_answer
    If the normal at \[\left( ct,\,\,\frac{c}{t} \right)\] on the curve\[xy={{c}^{2}}\] meets the curve again in\[V\] , 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 the tangent at\[\left( ct,\,\,\frac{c}{t} \right)\]is                 \[ty={{t}^{3}}x-c{{t}^{4}}+c\] If it passes through\[\left( ct',\,\,\frac{c}{t'} \right)\], then                 \[\frac{tc}{t'}={{t}^{3}}ct'-c{{t}^{4}}+c\] \[\Rightarrow \]               \[t={{t}^{3}}t{{'}^{2}}-{{t}^{4}}t'+t'\] \[\Rightarrow \]               \[t-t'={{t}^{3}}t'(t'-t)\] \[\Rightarrow \]               \[t'=\frac{1}{{{t}^{3}}}\]


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