JEE Main & Advanced Sample Paper JEE Main Sample Paper-47

  • question_answer
    For the curve, \[x={{t}^{2}}-1\], \[y={{t}^{2}}-t,\] the tangent line is perpendicular to x-axis, when

    A)  \[t=0\]           

    B)  \[t=\infty \]

    C)  \[t=\frac{1}{\sqrt{3}}\]                    

    D)  \[t=\frac{-1}{\sqrt{3}}\]

    Correct Answer: A

    Solution :

     Given, \[x={{t}^{2}}-1\] and \[y={{t}^{2}}-t\] Now, \[\frac{dx}{dt}=2t\] and \[\frac{dy}{dt}=2t-1\] \[\therefore \]    \[\frac{dy}{dx}=\frac{dy/dt}{dx/dt}=\frac{2t-1}{2t}\] \[\because \] The tangent line is perpendicular to x-axis. \[\therefore \]    \[\frac{dy}{dx}=\tan \,{{90}^{o}}=\infty =\frac{1}{0}\] \[\Rightarrow \]            \[\frac{2t-1}{2t}=\frac{1}{0}\] \[\Rightarrow \]            \[t=0\] where, \[\left( t\ne \frac{1}{2} \right)\]


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