N-order matrix a satisfies a & # 178; - 3A + 2E = 0, - prove that a-3e is an invertible matrix =Invertible matrix

N-order matrix a satisfies a & # 178; - 3A + 2E = 0, - prove that a-3e is an invertible matrix =Invertible matrix

I just see it.
Because a ^ 2-3a + 2E = 0
So a (a-3e) = - 2E
So a-3e is reversible and (a-3e) ^ - 1 = (- 1 / 2) a