Hi solving: Z^4+8z^3-9z^2=0 z^2(z^2 + 8z - 9)= 0 z^2= 0 z= 0 (z^2 + 8z - 9)= 0 factoring (z+9)(z-1)= 0 Note:SUM of the inner product(9z) and the outer product(-z) = 8z (z+9)=0 z = -9 (z-1)= 0 z = 1