JEE Main & Advanced Mathematics Pair of Straight Lines Question Bank Equation of Pair of Straight Lines

  • question_answer
    If \[4ab=3{{h}^{2}}\], then the ratio of slopes of the lines represented by the equation \[a{{x}^{2}}+2hxy+b{{y}^{2}}=0\] will be

    A)            \[\sqrt{2}:1\]                       

    B)            \[\sqrt{3}:1\]

    C)            \[2:1\]                                     

    D)            \[1:3\]

    Correct Answer: D

    Solution :

               Here \[{{m}_{1}}+{{m}_{2}}=\frac{-2h}{b}\]                                             .....(i)            and \[{{m}_{1}}{{m}_{2}}=\frac{a}{b}\]                                                       .....(ii)                    Also, given that \[4ab=3{{h}^{2}}.\]Now we have to find \[\frac{{{m}_{1}}}{{{m}_{2}}}\],                    therefore with the help of (i) and (ii), we get                    \[{{({{m}_{1}}-{{m}_{2}})}^{2}}=\frac{4{{h}^{2}}-4ab}{{{b}^{2}}}=\frac{4{{h}^{2}}-3{{h}^{2}}}{{{b}^{2}}}=\frac{{{h}^{2}}}{{{b}^{2}}}\]                    Þ \[{{m}_{1}}-{{m}_{2}}=\frac{h}{b}\]                                                                .....(iii) Now on solving (i) and (iii), we get                           \[{{m}_{1}}=\frac{-h}{2b}\]and \[{{m}_{2}}=\frac{-3h}{2b}\];  \\[{{m}_{1}}:{{m}_{2}}=1:3\].


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