JEE Main & Advanced Mathematics Pair of Straight Lines Question Bank Equation of lines joining the origin to the point of intersection of a curve and a line and Distance between the pair of lines

  • question_answer
    The lines joining the points of intersection of curve \[5{{x}^{2}}+12xy-8{{y}^{2}}+8x-4y+12=0\] and the line \[x-y=2\] to the origin , makes the angles with the axes

    A)            \[{{30}^{o}}\]and \[{{45}^{o}}\]                                      

    B)            \[{{45}^{o}}\] and \[{{60}^{o}}\]

    C)            Equal                                       

    D)            Parallel to axes

    Correct Answer: C

    Solution :

               We get the desired lines by homogenising the equation of curve w.r.t. line.       \[5{{x}^{2}}+12xy-8{{y}^{2}}+8x-4y+12=0\]            or \[5{{x}^{2}}+12xy-8{{y}^{2}}+(8x-4y)\left( \frac{x-y}{2} \right)+12\text{ }{{\left( \frac{x-y}{2} \right)}^{2}}=0\]            \[\Rightarrow 5{{x}^{2}}+12xy-8{{y}^{2}}+4{{x}^{2}}-4xy-2xy+2{{y}^{2}}+3{{x}^{2}}\]     \[+3{{y}^{2}}-6xy=0\]            \[\Rightarrow 12{{x}^{2}}-3{{y}^{2}}=0\] or \[4{{x}^{2}}-{{y}^{2}}=0\]            or \[(2x-y)(2x+y)=0\];       \[\therefore {{m}_{1}}=2,\ \ \ {{m}_{2}}=-2\].


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