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JAMIA MILLIA ISLAMIA Jamia Millia Islamia Solved Paper-2008

  • question_answer
        If the lines\[x+3y-9=0,4x+by-2=0\]and\[2x-y-4=0\]are concurrent, then b equals

    A)  \[-5\]                                   

    B)  5

    C)  1                                            

    D)  0

    Correct Answer: A

    Solution :

                    Since, the lines\[x+3y-9=0,\text{ }4x+by-2=0\] and\[2x-y-4=0\]are concurrent, then \[\left| \begin{matrix}    1 & 3 & -9  \\    4 & b & -2  \\    2 & -1 & -4  \\ \end{matrix} \right|=0\] \[\Rightarrow \] \[1(-4b-2)-3(-16+4)-9(-4-2b)=0\] \[\Rightarrow \]\[-4b-2+36+36+18b=0\] \[\Rightarrow \]\[14b+70=0\] \[\Rightarrow \] \[b=-5\]


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