Let a and B be square matrices of order n and E be identity matrices of order n. It is proved that if a + B = AB, then A-E is invertible

Let a and B be square matrices of order n and E be identity matrices of order n. It is proved that if a + B = AB, then A-E is invertible

A + B = AB, i.e
AB-A-B+E=E
(A-E)(B-E)=E
So A-E is reversible, and its inverse is b-e