JEE Main & Advanced Mathematics Conic Sections Question Bank Self Evaluation Test - Conic Sections

  • question_answer
    The value of m, for which the line \[y=mx+\frac{25\sqrt{3}}{3}\] is a normal to the conic \[\frac{{{x}^{2}}}{16}-\frac{{{y}^{2}}}{9}=1,\] is

    A) \[-\frac{2}{\sqrt{3}}\]

    B) \[\sqrt{3}\]

    C) \[-\frac{\sqrt{3}}{2}\]    

    D) None of these

    Correct Answer: A

    Solution :

    [a] The equation of normal to the hyperbola \[\frac{{{x}^{2}}}{{{a}^{2}}}-\frac{{{y}^{2}}}{{{b}^{2}}}=1\] in terms of slope ?m? is
    \[y=mx\pm \frac{m({{a}^{2}}+{{b}^{2}})}{\sqrt{{{a}^{2}}-{{b}^{2}}{{m}^{2}}}};\] Given line
    \[y=mx+\frac{25\sqrt{3}}{3}\]
    and coin \[\frac{{{x}^{2}}}{16}-\frac{{{y}^{2}}}{9}=1\] which is hyperbola
    with \[{{a}^{2}}=16,\,\,\,{{b}^{2}}=9\]
    By comparing given line with equation of normal we get
    \[\pm \frac{m({{a}^{2}}+{{b}^{2}})}{\sqrt{{{a}^{2}}-{{b}^{2}}{{m}^{2}}}}=+\frac{25\sqrt{3}}{3}\]
    \[\Rightarrow \frac{m(16+9)}{\sqrt{16-9{{m}^{2}}}}=-\frac{25\sqrt{3}}{3}\]
    \[\Rightarrow \frac{25m}{\sqrt{16-9{{m}^{2}}}}=-\frac{25\sqrt{3}}{3}\]
    \[\Rightarrow \,\,\,\,\,\,9\,{{m}^{2}}=3(16-9{{m}^{2}})\Rightarrow {{m}^{2}}=\frac{16}{12}=\frac{4}{3}\]    
    \[\Rightarrow m=\pm \frac{2}{\sqrt{3}}\]


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