If for an n ( n square matrix A, there is other n ( n square matrix B such that there product is the identity of the order n X n, In, i.e. A X B = B X A = I, then B is said to be inverse of A. Inverse if usually written as A-1
Hence AA-1 = I
Note: Only non singular matrices contain an inverse and therefore the inverse of a singular matrix is non-defined.