JEE Main & Advanced Sample Paper JEE Main Sample Paper-12

  • question_answer
    Ifs, s' are the length of the perpendicular on a tangent from the foci, a, a' are those from the vertices is that from the centre and e is the eccentricity of the ellipse, \[\frac{{{x}^{2}}}{{{a}^{2}}}+\frac{{{y}^{2}}}{{{b}^{2}}}=1,\]then \[\frac{ss'-{{c}^{2}}}{aa'-{{c}^{2}}}=\]

    A)  e                                           

    B)  1/e

    C)  \[1/{{e}^{2}}\]

    D)  \[{{e}^{2}}\]

    Correct Answer: D

    Solution :

     Let the equation of tangent\[y=mx+\sqrt{{{a}^{2}}{{m}^{2}}+{{b}^{2}}}\] Foci\[\equiv (\pm ae,0),vertices\equiv (\pm a,0),C\equiv (0,0)\] \[\therefore \]\[s=\left| \frac{mae+\sqrt{{{a}^{2}}{{m}^{2}}+{{b}^{2}}}}{\sqrt{1+m}} \right|,\] \[s'=\left| \frac{-mae+\sqrt{{{a}^{2}}{{m}^{2}}+{{b}^{2}}}}{\sqrt{1+{{m}^{2}}}} \right|\] \[a=\left| \frac{ma+\sqrt{{{a}^{2}}{{m}^{2}}+{{b}^{2}}}}{\sqrt{1+{{m}^{2}}}} \right|\] \[a'=\left| \frac{-ma+\sqrt{{{a}^{2}}{{m}^{2}}+{{b}^{2}}}}{\sqrt{1+{{m}^{2}}}} \right|,c=\left| \frac{\sqrt{{{a}^{2}}{{m}^{2}}+{{b}^{2}}}}{\sqrt{1+{{m}^{2}}}} \right|\] \[\therefore \]\[\frac{ss'-{{c}^{2}}}{aa'-{{c}^{2}}}=\frac{-\frac{{{m}^{2}}{{a}^{2}}{{e}^{2}}}{1+{{m}^{2}}}}{\frac{{{m}^{2}}{{a}^{2}}}{1+{{m}^{2}}}}={{e}^{2}}\]


You need to login to perform this action.
You will be redirected in 3 sec spinner