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

  • question_answer
    \[2{{x}^{2}}+7xy+3{{y}^{2}}+8x+14y+\lambda =0\] will represent a pair of straight lines, when \[\lambda \]=                                         [MP PET 1996]

    A)            2    

    B)            4

    C)            6    

    D)            8

    Correct Answer: D

    Solution :

               \[(2)(3)(\lambda )+2(7)(4)\frac{7}{2}-2{{(7)}^{2}}-3{{(4)}^{2}}-\lambda {{\left( \frac{7}{2} \right)}^{2}}=0\]                                 \[\Rightarrow 6\lambda +196-98-48-\frac{49\lambda }{4}=0\Rightarrow \lambda =8\].


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