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

  • question_answer
    If the slope of one line of the pair of lines represented by \[a{{x}^{2}}+4xy+{{y}^{2}}=0\]is 3 times the slope of the other line, then a is                                                                                                     [DCE 1999]

    A)            1    

    B)            2

    C)            3    

    D)            4

    Correct Answer: C

    Solution :

               Here \[{{m}_{1}}+{{m}_{2}}=-4\]                                   ..... (i)                    and \[{{m}_{1}}\,{{m}_{2}}=a\]                                                               .?.(ii)                    Given that\[{{m}_{1}}=3{{m}_{2}}\].                    By (i), \[3{{m}_{2}}+{{m}_{2}}=-4\]Þ \[{{m}_{2}}=-1\]                    Hence, \[{{m}_{1}}=-3\]. Now, by (ii) \[a=3.\]


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