JEE Main & Advanced JEE Main Paper (Held On 11-Jan-2019 Evening)

  • question_answer
    Let the length of the latus rectum of an ellipse with its major axis along x-axis and centre at the origin, be 8. If the distance between the foci of this ellipse is equal to the length of its minor axis, then which one of the following points lies on it? [JEE  Main Online Paper (Held on 11-jan-2019 Evening)]

    A) \[(4\sqrt{2},2\sqrt{3})\]                          

    B) \[(4\sqrt{3},2\sqrt{3})\]

    C) \[(4\sqrt{2},2\sqrt{2})\]                          

    D) \[(4\sqrt{3},2\sqrt{2})\]

    Correct Answer: D

    Solution :

    Let the equation of the ellipse is\[\frac{{{x}^{2}}}{{{a}^{2}}}+\frac{{{y}^{2}}}{{{b}^{2}}}=1\] \[\therefore \]\[\frac{2{{b}^{2}}}{a}=8\Rightarrow {{b}^{2}}=4a\]and\[2ae=2b\Rightarrow e=\frac{b}{a}\] Since,\[{{e}^{2}}=1-\frac{{{b}^{2}}}{{{a}^{2}}}\] \[\Rightarrow \]\[{{e}^{2}}=1-{{e}^{2}}\]\[\Rightarrow \]\[e=\frac{1}{\sqrt{2}}\] Now,\[\frac{1}{2}=1-\frac{4a}{{{a}^{2}}}\Rightarrow a=8\]and\[b=ae=8.\frac{1}{\sqrt{2}}=4\sqrt{2}\] \[\therefore \] Equation of ellipse is\[\frac{{{x}^{2}}}{64}+\frac{{{y}^{2}}}{32}=1\] The point only in option i.e., \[(4\sqrt{3},2\sqrt{2})\]lies on the ellipse.


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