(A−1)−1=A\left(A^{-1}\right)^{-1}=A(A−1)−1=A
(AB)−1=A−1 B−1(\mathrm{AB})^{-1}=\mathrm{A}^{-1} \mathrm{~B}^{-1}(AB)−1=A−1 B−1
(AT)−1=(A−1)T\left(A^{T}\right)^{-1}=\left(A^{-1}\right)^{T}(AT)−1=(A−1)T
(BA)A−1=B(B A) A^{-1}=B(BA)A−1=B
