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

  • question_answer
    If \[\frac{{{x}^{2}}}{a}+\frac{{{y}^{2}}}{b}+\frac{2xy}{h}=0\] represent pair of straight lines and slope of one line is twice the other. Then \[ab:{{h}^{2}}\] is [DCE 2005]

    A)            9 : 8                                          

    B)            8 : 9

    C)            1 : 2                                          

    D)            2 : 1

    Correct Answer: A

    Solution :

               Let \[{{m}_{1}},{{m}_{2}}\] be the slopes                    \[\therefore \]\[{{m}_{1}}+{{m}_{2}}=-\frac{2b}{h}\] and \[{{m}_{1}}{{m}_{2}}=\frac{b}{a}\]                    Again\[{{m}_{2}}\] =\[2{{m}_{1}}\]                    \[\therefore \]\[3{{m}_{1}}=-\frac{2b}{h}\] and \[2m_{1}^{2}=\frac{b}{a}\]            \[\therefore \]\[\frac{9m_{1}^{2}}{2m_{1}^{2}}=\frac{4{{b}^{2}}}{{{h}^{2}}}\times \frac{a}{b}\Rightarrow ab:{{h}^{2}}=9:8\].


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