x(kT)=∑res[1/(1-z^2)*z^(k-1)]=1/[(1-z)(1+z)]=∑res{1/[(1-z)(1+z)]*z^(k-1)}=1/[(1-z)(1+z)]*z^(k-1)*(z-1)|(z=1)+1/[(1-z)(1+z)]*z^(k-1)*(z+1)|(z=-1)=(-1)^(k-1)/2-1/2 k=0,1,2……
