JEE Main & Advanced Mathematics Conic Sections Question Bank Parabola

  • question_answer
    The equation of the tangent to the parabola \[{{y}^{2}}=16x\], which is perpendicular to the line \[y=3x+7\] is               [MP PET 1998]

    A)            \[y-3x+4=0\]                             

    B)            \[3y-x+36=0\]

    C)            \[3y+x-36=0\]                           

    D)            \[3y+x+36=0\]

    Correct Answer: D

    Solution :

               Line perpendicular to given line, \[3y+x=\lambda \]                    \[y=\frac{-1}{3}x+\frac{\lambda }{3}\].                    Here, \[m=\frac{-1}{3},\,\,c=\frac{\lambda }{3}\]                    If we compare \[{{y}^{2}}=16x\] with \[{{y}^{2}}=4ax\] then \[a=4\],                    Condition for tangency is,                    \[c=\frac{a}{m}\Rightarrow \frac{\lambda }{3}=\frac{4}{(-1/3)}\Rightarrow \lambda =-36\]                    Required equation is; \[x+3y+36=0\].


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