JAMIA MILLIA ISLAMIA Jamia Millia Islamia Solved Paper-2008

  • question_answer
        If\[2A+3B=\left[ \begin{matrix}    2 & -1 & 4  \\    3 & 2 & 5  \\ \end{matrix} \right]\]and\[A+2B=\left[ \begin{matrix}    5 & 0 & 3  \\    1 & 6 & 2  \\ \end{matrix} \right],\]then B is

    A)  \[\left[ \begin{matrix}    8 & -1 & 2  \\    -1 & 10 & -1  \\ \end{matrix} \right]\]   

    B)  \[\left[ \begin{matrix}    8 & 1 & 2  \\    -1 & 10 & -1  \\ \end{matrix} \right]\]

    C)  \[\left[ \begin{matrix}    8 & 1 & -2  \\    -1 & 10 & -1  \\ \end{matrix} \right]\]   

    D)  \[\left[ \begin{matrix}    8 & 1 & 2  \\    1 & 10 & 1  \\ \end{matrix} \right]\]

    Correct Answer: B

    Solution :

                    We have \[2A+3B=\left[ \begin{matrix}    2 & -1 & 4  \\    3 & 2 & 5  \\ \end{matrix} \right]\]                    ?.(i) and        \[A+2B=\left[ \begin{matrix}    5 & 0 & 3  \\    1 & 6 & 2  \\ \end{matrix} \right]\]                     ...(ii) Multiply Eq. (ii) by 2 and subtracting Eq.(i) from (ii), we get                 \[B=2\left[ \begin{matrix}    5 & 0 & 3  \\    1 & 6 & 2  \\ \end{matrix} \right]-\left[ \begin{matrix}    2 & -1 & 4  \\    3 & 2 & 5  \\ \end{matrix} \right]\]                 \[=\left[ \begin{matrix}    8 & 1 & 2  \\    -1 & 10 & -1  \\ \end{matrix} \right]\]


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