4. compute the characteristic polynomial of the following matrices. that is, compute the poly- nomial det (a -ai) where i is the identity matrix. o a-b3 1 0-11 (b) b-2 2 1 1 0 1 e) for the characteristic polynomial obtained in part a), replace all occurences of ? with the matrix a, and replace any constants c by e/ where i is the 2 x 2 identity matrix. what is the resulting 2 x 2 matrix? repeat this for part (b) and the matrix b.