确定有理z变换的因式分解形式，并确定零极点,根据零极点确定有理z变换的表达式,部分分式展开的方法求逆z变换,用长除法求逆z变换,完成系统的稳定性判断-Z transformation to determine justified factorization form, and to determine zero-pole, according to zero-pole z transformation to determine justified the expression, partial fraction methods to start z inverse transform, using long division inverse z transform, the completion of system stability judge