**Theorem 2.1.5.**


In linear algebra invertible matrix are important. From the problem of eigenvalues we can easily conclude If the matrix *A* is invertible or not. What more can be, the eigenvalues of the matrix *A* invertible can be immediately read from the eigenvalues of the matrix *A*− 1. Because of that, in the following theorems we summarize some properties of invertible matrix.
