467 Appendix A Solritiolts t,o t,he Excrciscs ~ o l u t i Q1.6 i~ vlic know from that tlir system is not linear and tiiw-invnriaiit at tlu barne h i e It c.oiild however b~ ritticr one of the two, arid it is not possible to say w1iic.h olutiori 2.1 a) Show that QL 2=0 Substitutiiig vmiahles 1' = - + rlt' = dt d ( t - r) - the sulxtitution leads to thc above equation 1)) Tf 91 is the spstwn response to r1 and s/2 dt the response to x2: dr' = df' ie.,