逆行列
$ A=\left(\begin{array}{ll}{a} & {b} \\ {c} & {d}\end{array}\right)の逆行列は$ A^{-1}=\frac{1}{a d-b c}\left(\begin{array}{cc}{d} & {-b} \\ {-c} & {a}\end{array}\right)
$ AA^{-1}=E.
掃き出し法を用いて求める
$ (A I)=\left(\begin{array}{cccccc}{1} & {1} & {-1} & {1} & {0} & {0} \\ {-2} & {0} & {1} & {0} & {1} & {0} \\ {0} & {2} & {1} & {0} & {0} & {1}\end{array}\right)
参考