527 Appeiidix A Solutions to the Exercises k g) L TI, because S{:r[k- N ] } = :r[p- Nj = 11) L L I , becausr difference equatioiis describe LTI systems i) I,, not, Tl, see d) j ) TI, not I,, bemuse + S { x l [ k ] ~ [ k ] } = u ~ ~ ~ ~ ]#+ ” ~ [ ~ - ] S{r1[l;]) + S { Q [ k ] ) = a.””kl + aJ:zlkl