Find the inverse of A=(2111)A = \begin{pmatrix} 2 & 1 \\ 1 & 1 \end{pmatrix}A=(2111).
(1−1−12)\begin{pmatrix} 1 & -1 \\ -1 & 2 \end{pmatrix}(1−1−12)
(1111)\begin{pmatrix} 1 & 1 \\ 1 & 1 \end{pmatrix}(1111)
(2−1−12)\begin{pmatrix} 2 & -1 \\ -1 & 2 \end{pmatrix}(2−1−12)
(12−12−1212)\begin{pmatrix} \frac{1}{2} & -\frac{1}{2} \\ -\frac{1}{2} & \frac{1}{2} \end{pmatrix}(21−21−2121)