If A is a square matrix, then the products AA, AAA, AAAA,… are defined, and these powers of A are denoted by A2, A3, A4,…. For all positive integers p and q,
By definition, A0 = I. Moreover, if A is invertible, then A2, A3,…are invertible, and it can be shown that (A−1)p is the inverse of Ap, so that (A−1)p = (Ap)−1. So either of these is denoted by A−p. Thus, when A is invertible, Ap has been defined for all integers and properties (i) and (ii) above hold for all integers p and q.