CEE Kerala Engineering CEE Kerala Engineering Solved Paper-2005

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

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

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

    C)  \[nm-1=0\]       

    D)         \[nm+1=0\]

    E)  \[\frac{1}{m}-\frac{1}{n}=0\]

    Correct Answer: D

    Solution :

    Equation of bisectors of angles between \[{{x}^{2}}-2nxy-{{y}^{2}}=0\]is \[\frac{{{x}^{2}}-{{y}^{2}}}{1+1}=\frac{xy}{-n}\] \[{{x}^{2}}+\frac{2}{n}xy+{{y}^{2}}=0\]          ...(i) This equation is identical to \[{{x}^{2}}-2mxy-{{y}^{2}}=0\] \[\therefore \]  \[\frac{\frac{2}{n}}{-2m}=1\] \[\Rightarrow \]               \[\frac{1}{n}=-m\] \[\Rightarrow \]               \[mn+1=0\]


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