k ∈ N. Therefore, it follows from our results in Step 1 that pk (Ak ) = 0, where pk (λ) = det(λI − Ak ) denotes the characteristic polynomial of Ak .
Note that each entry of the matrix p(A) can be written as a polynomial in the entries of A. Since limk→∞ Ak = A, we conclude that limk→∞ pk (Ak ) = p(A). Since pk (Ak ) = 0 for every k ∈ N, we must have p(A) = 0.