JEE Main & Advanced Mathematics Conic Sections Question Bank Ellipse

  • question_answer
    The equation of the ellipse whose foci are \[(\pm 5,\ 0)\] and one of its directrix is \[5x=36\], is

    A)            \[\frac{{{x}^{2}}}{36}+\frac{{{y}^{2}}}{11}=1\]                            

    B)            \[\frac{{{x}^{2}}}{6}+\frac{{{y}^{2}}}{\sqrt{11}}=1\]

    C)            \[\frac{{{x}^{2}}}{6}+\frac{{{y}^{2}}}{11}=1\]                              

    D)            None of these

    Correct Answer: A

    Solution :

               Foci \[(\pm 5,\,0)\equiv (\pm ae,\,0)\]. Directrix \[\left( x=\frac{36}{5} \right)\equiv x=\frac{a}{e}\]            So, \[\frac{a}{e}=\frac{36}{5},\ ae=5\] Þ \[a=6\] and \[e=\frac{5}{6}\]            Therefore, \[b=6\sqrt{1-\frac{25}{36}}=6\frac{\sqrt{11}}{6}=\sqrt{11}\]            Hence equation is\[\frac{{{x}^{2}}}{36}+\frac{{{y}^{2}}}{11}=1\].


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