JEE Main & Advanced Mathematics Pair of Straight Lines Question Bank Angle between the pair of straight lines, Condition for parallel and perpendicular lines

  • question_answer
    The straight lines joining the origin to the points of intersection of the line \[2x+y=1\] and curve \[3{{x}^{2}}+4xy-4x+1=0\] include an angle                              [MP PET 1993]

    A)            p/2

    B)            p/3

    C)            p/4

    D)            p/6

    Correct Answer: A

    Solution :

               Making equation of curve homogeneous w.r.t. line \[3{{x}^{2}}+4xy-4x(2x+y)+{{(2x+y)}^{2}}=0\]            \[\Rightarrow 3{{x}^{2}}+4xy-8{{x}^{2}}-4xy+4{{x}^{2}}+{{y}^{2}}+4xy=0\]            \[\Rightarrow {{x}^{2}}-4xy-{{y}^{2}}=0\]            Angle between these two lines is \[\tan \theta =\frac{2\sqrt{{{h}^{2}}-ab}}{a+b}\] \[=\frac{2\sqrt{4+1}}{0}=\infty \] i.e., lines are perpendicular.


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