JEE Main & Advanced AIEEE Solved Paper-2002

  • question_answer
    The radius of the circle passing through the foci of the ellipse \[\frac{{{x}^{2}}}{16}+\frac{{{y}^{2}}}{9}\] and having its centre at (0, 3), is

    A) 4 units

    B)           3 units     

    C)           \[\sqrt{12}\] units              

    D)           \[\frac{7}{2}\] units

    Correct Answer: A

    Solution :

       Eccentricity \[(e)=\sqrt{1-\frac{{{a}^{2}}}{{{b}^{2}}}}\] and foci are \[S(+ae.0)\] and \[{{S}_{1}}(-ae,0)\]. The equation of an ellipse is                    \[\frac{{{x}^{2}}}{16}+\frac{{{y}^{2}}}{9}=1\] Here, \[a=4,\,b=3\] \[\therefore \]     \[e=\sqrt{1-\frac{{{b}^{2}}}{{{a}^{2}}}}\]                    \[=\sqrt{1-\frac{9}{16}}=\frac{\sqrt{7}}{4}\] \[\therefore \] Foci of an ellipse are \[(\pm \sqrt{7},0)\]. \[\therefore \] Radius of required circle                                    \[=\sqrt{{{(\sqrt{7}-0)}^{2}}+{{(0-3)}^{2}}}\]                                    \[=\sqrt{7+9}\]                                    \[=\sqrt{16}=4\] units


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