JEE Main & Advanced JEE Main Paper (Held On 16 April 2018)

  • question_answer
    The locus of the point of intersection of the lines,\[\sqrt{2x}-y+4\sqrt{2k}=0\]and \[\sqrt{2}kx+ky-4\sqrt{2}=0\](k is any non-zero real parameter), is?     [JEE Main 16-4-2018]

    A)  A hyperbola with length of its transeverse axis\[8\sqrt{2}\]

    B)  An ellipse with length of its major axis \[8\sqrt{2}\]

    C)  An ellipse whose eccentricity is \[\frac{1}{\sqrt{3}}\]

    D)  A hyperbola whose eccentricity is \[\sqrt{3}\]

    Correct Answer: A

    Solution :

     Gives lines are:                 \[\sqrt{2x}-y+4\sqrt{2k}=0\] \[\Rightarrow \]\[\sqrt{2x}+4\sqrt{2k}=y\]                             ??(i) and \[\sqrt{2kx}+ky-4\sqrt{2}=0\]?.. (ii) We have from the equations of the lines: Substituting (i) in                                       (ii), \[\Rightarrow 2\sqrt{2}kx+4\sqrt{2}({{k}^{2}}-1)=0\]  \[\Rightarrow \]\[x=\frac{1(1-{{k}^{2}})}{k},y=\frac{2\sqrt{2}(1+{{k}^{2}})}{k}\] \[\Rightarrow \]\[{{\left( \frac{y}{4\sqrt{2}} \right)}^{2}}-{{\left( \frac{x}{4} \right)}^{2}}=1\] \[\Rightarrow \]\[{{\left( \frac{y}{4\sqrt{2}} \right)}^{2}}-{{\left( \frac{x}{4} \right)}^{2}}=1\]                      Locus of transverse axis \[=2\sqrt{32}\] \[=2\times 4\sqrt{2}\] \[=8\sqrt{2}\] Thus, the locus is a hyperbola with length of its transverse axis equal to\[8\sqrt{2}.\] So option A is the correct answer.


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