2.3用长除法、留数定理、部分分式法试求以下X(z)的z反变换。-|||-(1) (z)=dfrac (1-dfrac {1)(2)(z)^-1}(1-dfrac {1)(4)(z)^-2} - |z|gt dfrac (1)(2)-|||-(2) (z)=dfrac (1-2{z)^-1}(1-dfrac {1)(4)(z)^-1} . |z|lt dfrac (1)(4)-|||-(3) (z)=dfrac ({z)^-1-a}(1-a{z)^-1} , |z|gt a-|||-(4) (z)=dfrac (1-dfrac {1)(4)(z)^-1}(1-dfrac {8)(15)(z)^-1+dfrac (1)(15)(z)^-2} ..dfrac (1)(5)lt |z|lt dfrac (1)(3)