JEE Main & Advanced Mathematics Conic Sections Question Bank Ellipse

  • question_answer
    Eccentric angle of a point on the ellipse \[{{x}^{2}}+3{{y}^{2}}=6\] at a distance 2 units from the centre of the ellipse is [WB JEE 1990]

    A)            \[\frac{\pi }{4}\]

    B)            \[\frac{\pi }{3}\]

    C)            \[\frac{3\pi }{4}\]                     

    D)            \[\frac{2\pi }{3}\]

    Correct Answer: A

    Solution :

     Let the eccentric angle of the point be\[\theta \], then its     co-ordinates are \[(\sqrt{6}\cos \theta ,\sqrt{2}\sin \theta ).\]            Hence \[6{{\cos }^{2}}\theta +2{{\sin }^{2}}\theta =4\]or \[{{\cos }^{2}}\theta =\frac{1}{2}\]                    Hence, \[\cos \theta =\pm \frac{1}{\sqrt{2}}\], \\[\theta =\frac{\pi }{4}\]or \[\frac{3\pi }{4}\].


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