JEE Main & Advanced JEE Main Paper (Held On 11 April 2015)

  • question_answer
    If the distance between the foci of an ellipse is half the length of its latus rectum, then the eccentricity of the ellipse is : [JEE Main Online Paper (Held On 11 April 2015)]  

    A) \[\frac{1}{2}\]

    B) \[\frac{2\sqrt{2}-1}{2}\]

    C) \[\sqrt{2}-1\]

    D) \[\frac{\sqrt{2}-1}{2}\]

    Correct Answer: C

    Solution :

      \[2ae=\frac{1}{2}\left( \frac{2{{b}^{2}}}{a} \right)\]\[\Rightarrow \]\[2ae=\frac{{{b}^{2}}}{a}\]\[\Rightarrow \]\[2e=\frac{{{b}^{2}}}{{{a}^{2}}}\] also\[{{e}^{2}}=1-\frac{{{b}^{2}}}{{{a}^{2}}}\Rightarrow {{e}^{2}}=1-2e\Rightarrow e=\sqrt{2}-1\]


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