JEE Main & Advanced Mathematics Conic Sections Question Bank Ellipse

  • question_answer
    If the foci of an ellipse are \[(\pm \sqrt{5},\,0)\] and its eccentricity is \[\frac{\sqrt{5}}{3}\], then the equation of the ellipse is  [J & K 2005]

    A)            \[9{{x}^{2}}+4{{y}^{2}}=36\]     

    B)            \[4{{x}^{2}}+9{{y}^{2}}=36\]

    C)            \[36{{x}^{2}}+9{{y}^{2}}=4\]    

    D)            \[9{{x}^{2}}+36{{y}^{2}}=4\]

    Correct Answer: B

    Solution :

                       \[\because \,ae=\pm \sqrt{5}\] Þ \[a=\pm \sqrt{5}\left( \frac{3}{\sqrt{5}} \right)=\pm 3\] Þ \[{{a}^{2}}=9\]                    \\[{{b}^{2}}={{a}^{2}}(1-{{e}^{2}})=9\left( 1-\frac{5}{9} \right)=4\]                    Hence, equation of ellipse\[\frac{{{x}^{2}}}{9}+\frac{{{y}^{2}}}{4}=1\]Þ \[4{{x}^{2}}+9{{y}^{2}}=36\].


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