JCECE Engineering JCECE Engineering Solved Paper-2012

  • question_answer
    If\[A=\left[ \begin{matrix}    1 & 2  \\    2 & 1  \\ \end{matrix} \right]\]and\[f(x)=\frac{1+x}{1-x}\], find the value of\[f(A)\].

    A) \[\left[ \begin{matrix}    1 & 1  \\    1 & 1  \\ \end{matrix} \right]\]                   

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

    C) \[\left[ \begin{matrix}    2 & 2  \\    2 & 2  \\ \end{matrix} \right]\]                   

    D)  None of these

    Correct Answer: B

    Solution :

    We have,\[f(x)=\frac{1+x}{1-x}\] \[\therefore \]  \[f(A)=\frac{I+A}{I-A}\]                 \[=(I+A){{(I-A)}^{-1}}\]                 \[=\left[ \begin{matrix}    2 & 2  \\    2 & 2  \\ \end{matrix} \right]{{\left[ \begin{matrix}    0 & -2  \\    -2 & 0  \\ \end{matrix} \right]}^{-1}}\] \[\Rightarrow \]\[f(A)=\left[ \begin{matrix}    2 & 2  \\    2 & 2  \\ \end{matrix} \right]\left[ \begin{matrix}    0 & -1/2  \\    -1/2 & 0  \\ \end{matrix} \right]\]                 \[=\left[ \begin{matrix}    -1 & -1  \\    -1 & -1  \\ \end{matrix} \right]\]


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