Let a be a square matrix of order n, AA = a, and prove that R (a) + R (A-E) = n

Let a be a square matrix of order n, AA = a, and prove that R (a) + R (A-E) = n


(1) A ^ 2 = a, so a (A-E) = 0, so r (a) + R (A-E) = R (a + e-A) = R (E) = n
So r (a) + R (A-E) = n