Let the matrix a be a normal matrix and satisfy the cubic power of a = the quadratic power of 2A. It is proved that the quadratic power of a = 2A

Let the matrix a be a normal matrix and satisfy the cubic power of a = the quadratic power of 2A. It is proved that the quadratic power of a = 2A

A matrix is normal if and only if it can be unitary diagonalized
Let a = UDU ^ t be substituted into known UDU ^ 3U ^ t = 2ud ^ 2U ^ t, so d ^ 3 = 2D ^ 2
So for any eigenvalue D, d ^ 3 = 2D ^ 2, this condition can deduce d ^ 2 = 2D, so d ^ 2 = 2D, so a ^ 2 = 2A