Let K {\displaystyle {}K} be a field, and let M {\displaystyle {}M} denote an n × n {\displaystyle {}n\times n} -matrix over K {\displaystyle {}K} . Then M {\displaystyle {}M} is called invertible, if there exists a matrix A ∈ Mat n ( K ) {\displaystyle {}A\in \operatorname {Mat} _{n}(K)} such that
holds.