CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2006

  • question_answer
    If the two pair of lines\[{{x}^{2}}-2mxy-{{y}^{2}}=0\]and \[{{x}^{2}}-2nxy-{{y}^{2}}=0\]are such that one of them represents the bisector of the angles between the other, then:

    A)  \[mn+1=0\]

    B)         \[mn-1=0\]

    C)  \[\frac{1}{m}+\frac{1}{n}=0\]     

    D)         \[\frac{1}{m}-\frac{1}{n}=0\]

    E)  none of these

    Correct Answer: A

    Solution :

          Equation of the bisectors of the angle between the lines\[{{x}^{2}}-2nxy-{{y}^{2}}=0\]are given by \[\frac{{{x}^{2}}-{{y}^{2}}}{1-(-1)}=\frac{xy}{-m}\Rightarrow {{x}^{2}}+\frac{2}{m}xy-{{y}^{2}}=0\]?(i) Since, (i) and\[{{x}^{2}}-2nxy-{{y}^{2}}=0\]represents the same pair of lines. \[\therefore \]  \[\frac{1}{1}=\frac{\frac{2}{m}}{-n}\] \[\Rightarrow \]               \[mn=-1\Rightarrow mn+1=0\]


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