Appendix A Solutions to the Exercises 543 = l,(t) -sin(Gt) = -u(t) Solution 16.9 a) H ( s ) has poles at s = fj c) s2 - Xs + must be a Hurwitz po1yriomi;tl + K h, ( t ) is intrgrablc Solution 16.10 a) + unstable i stahlP < (1