RAJASTHAN ­ PET Rajasthan PET Solved Paper-2002

  • question_answer
    If equation of latusrectum of a parabola is \[x+y=8\]and equation of tangent at its vertex is\[x+y=12,\]then length of its latusrectum is

    A)  \[4\sqrt{2}\]

    B)  \[2\sqrt{2}\]

    C)  \[8\]

    D)  \[8\sqrt{2}\]

    Correct Answer: D

    Solution :

     Equations of given lines \[x+y=8\]                     ...(i) and     \[x+y=12\]                   ...(ii) Both of these lines are mutually perpendicular \[\therefore \]Distance between the parallel lines \[\left| \frac{{{c}_{1}}-{{c}_{2}}}{\sqrt{{{a}^{2}}+{{b}^{2}}}} \right|=\left| \frac{12-8}{\sqrt{1+1}} \right|\] \[=\frac{4}{\sqrt{2}}=2\sqrt{2}\] \[\therefore \] \[a=2\sqrt{2}\] Hence, length of latusrectum\[=4a\] \[=4\times 2\sqrt{2}=8\sqrt{2}\]


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