JEE Main & Advanced JEE Main Paper Phase-I (Held on 09-1-2020 Evening)

  • question_answer
    The length of the minor axis (along y-axis) of an ellipse in the standard form is \[\frac{4}{\sqrt{3}}.\] If this ellipse touches the line, \[x+6y=8;\] then its eccentricity is [JEE MAIN Held on 09-01-2020 Evening]

    A) \[\frac{1}{3}\sqrt{\frac{11}{3}}\]

    B) \[\frac{1}{2}\sqrt{\frac{5}{3}}\]

    C) \[\sqrt{\frac{5}{6}}\]

    D) \[\frac{1}{2}\sqrt{\frac{11}{3}}\]

    Correct Answer: D

    Solution :

    \[2b=\frac{4}{\sqrt{3}}\,\,\Rightarrow \,\,{{b}^{2}}=\frac{4}{3}\]   Equation of tangent to ellipse \[\frac{{{x}^{2}}}{{{a}^{2}}}+\frac{{{y}^{2}}}{{{b}^{2}}}=1\] is \[y=mx\pm \sqrt{{{a}^{2}}{{m}^{2}}+{{b}^{2}}},\] here \[m=-\frac{1}{6}\] so equation of tangent is \[y=-\frac{x}{6}\pm \sqrt{\frac{{{a}^{2}}}{36}+\frac{4}{3}}\] But \[x+6y=8\] is given to be a tangent So after comparing we get \[a=4\] Now \[e=\sqrt{1-\frac{{{b}^{2}}}{{{a}^{2}}}}=\sqrt{\frac{11}{12}}\]


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