By using elementary operations,find the inverse of the matrix $A=\left[\begin{array}{rr}1 & 2 \\ 2 & -1\end{array}\right]$.

  • A
    $A^{-1}=\left[\begin{array}{ll}\frac{1}{5} & \frac{2}{5} \\ \frac{2}{5} & \frac{-1}{5}\end{array}\right]$
  • B
    $A^{-1}=\left[\begin{array}{ll}\frac{1}{5} & \frac{2}{5} \\ \frac{2}{5} & \frac{1}{5}\end{array}\right]$
  • C
    $A^{-1}=\left[\begin{array}{ll}\frac{1}{5} & \frac{-2}{5} \\ \frac{-2}{5} & \frac{-1}{5}\end{array}\right]$
  • D
    $A^{-1}=\left[\begin{array}{ll}\frac{-1}{5} & \frac{2}{5} \\ \frac{2}{5} & \frac{1}{5}\end{array}\right]$

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