JEE Main & Advanced Mathematics Conic Sections Question Bank Ellipse

  • question_answer
    The line \[lx+my-n=0\] will be tangent to the ellipse \[\frac{{{x}^{2}}}{{{a}^{2}}}+\frac{{{y}^{2}}}{{{b}^{2}}}=1\], if

    A)            \[{{a}^{2}}{{l}^{2}}+{{b}^{2}}{{m}^{2}}={{n}^{2}}\]                     

    B)            \[a{{l}^{2}}+b{{m}^{2}}={{n}^{2}}\]

    C)            \[{{a}^{2}}l+{{b}^{2}}m=n\]      

    D)            None of these

    Correct Answer: A

    Solution :

               \[y=\frac{-l}{m}x+\frac{n}{m}\]is tangent to \[\frac{{{x}^{2}}}{{{a}^{2}}}+\frac{{{y}^{2}}}{{{b}^{2}}}=1\], if             \[\frac{n}{m}=\pm \sqrt{{{b}^{2}}+{{a}^{2}}{{\left( \frac{l}{m} \right)}^{2}}}\] or\[{{n}^{2}}={{m}^{2}}{{b}^{2}}+{{l}^{2}}{{a}^{2}}\].


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