JEE Main & Advanced Mathematics Conic Sections Question Bank Ellipse

  • question_answer
    What is the equation of the ellipse with foci \[(\pm 2,\ 0)\] and eccentricity \[=\frac{1}{2}\]          [DCE 1999]

    A)            \[3{{x}^{2}}+4{{y}^{2}}=48\]     

    B)            \[4{{x}^{2}}+3{{y}^{2}}=48\]

    C)            \[3{{x}^{2}}+4{{y}^{2}}=0\]       

    D)            \[4{{x}^{2}}+3{{y}^{2}}=0\]

    Correct Answer: A

    Solution :

               Since, \[ae=\pm \,2\] \[\Rightarrow \,a=\pm \,4\]   \[(\because \,\,e=1/2)\] Now \[{{b}^{2}}={{a}^{2}}(1-{{e}^{2}})\]\[\Rightarrow \]\[{{b}^{2}}=16(1-1/4)\]\[\Rightarrow \]\[{{b}^{2}}=12\] Hence ellipse is\[\frac{{{x}^{2}}}{16}+\frac{{{y}^{2}}}{12}=1\]\[\Rightarrow \]\[3{{x}^{2}}+4{{y}^{2}}=48\].


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