Given A=(2111)A = \begin{pmatrix} 2 & 1 \\ 1 & 1 \end{pmatrix}A=(2111), which of the following is the inverse matrix A−1A^{-1}A−1?
(1−1−12)\begin{pmatrix} 1 & -1 \\ -1 & 2 \end{pmatrix}(1−1−12)
(1112)\begin{pmatrix} 1 & 1 \\ 1 & 2 \end{pmatrix}(1112)
(−111−2)\begin{pmatrix} -1 & 1 \\ 1 & -2 \end{pmatrix}(−111−2)
(2−1−11)\begin{pmatrix} 2 & -1 \\ -1 & 1 \end{pmatrix}(2−1−11)