JEE Main & Advanced Mathematics Conic Sections Question Bank Parabola

  • question_answer
    The equation of the tangent to the parabola \[{{y}^{2}}=4ax\] at point \[(a/{{t}^{2}},\ 2a/t)\] is     [RPET 1996]

    A) \[ty=x{{t}^{2}}+a\]                               

    B) \[ty=x+a{{t}^{2}}\]

    C) \[y=tx+a{{t}^{2}}\]                               

    D) \[y=tx+(a/{{t}^{2}})\]

    Correct Answer: A

    Solution :

    Equation of the tangent to the parabola, \[{{y}^{2}}=4ax\] is \[y{{y}_{1}}=2a(x+{{x}_{1}})\] Þ  \[y.\frac{2a}{t}=2a\left( x+\frac{a}{{{t}^{2}}} \right)\] Þ \[\frac{y}{t}=\left( x+\frac{a}{{{t}^{2}}} \right)\ Þ\[\frac{y}{t}=\frac{{{t}^{2}}x+a}{{{t}^{2}}}\] Þ \[ty={{t}^{2}}x+a\]


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