Find the characteristic polynomial of the matrix, using either a cofactor expansion or the special formula for 3x3 determinants. [Note: Finding the characteristic polynomial of a 3 x 3 matrix is not easy to do with just row operations, because the variable 2. is involved.] 1 0 1 - 2 3 -1 0 7 0 . The characteristic polynomial is (Type an expression using a as the variable.)