JAMIA MILLIA ISLAMIA Jamia Millia Islamia Solved Paper-2009

  • question_answer
        If the pair of straight lines\[a{{x}^{2}}+2hxy-a{{y}^{2}}=0\] and \[b{{x}^{2}}+2gxy-b{{y}^{2}}=0,\]be such that each bisect the angle between the other, then

    A)  \[hg+ab=0\]                     

    B)  \[ah+bg=0.\]

    C)  \[{{h}^{2}}-ab=0\]         

    D)  \[ag+bh=0.\]

    Correct Answer: A

    Solution :

                    Since, each pair of line bisect the angle between the other. So, the equation of bisectors of the angles between the line given by \[a{{x}^{2}}+2hxy-a{{y}^{2}}=0\]is \[b{{x}^{2}}+2gxy-b{{y}^{2}}=0\]         ...(i) But the equation of bisector of the angle between the line given by \[a{{x}^{2}}+2hxy-a{{y}^{2}}=0\]is                 \[\frac{{{x}^{2}}-{{y}^{2}}}{a-(-a)}=\frac{xy}{h}\] \[\Rightarrow \]               \[h{{x}^{2}}-2axy-h{{y}^{2}}=0\]                        ...(ii) Since, lines (i) and (ii) represents the same pair of straight lines, therefore                 \[\frac{b}{h}=\frac{g}{-a}=\frac{-b}{-h}\] \[\Rightarrow \]               \[-ab=gh\] \[\Rightarrow \]               \[ab+gh=0\]


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