请问一下这个是哪个知识点呀？谢谢老师

问题如下：

a. What conditions must k and m satisfy for the first difference series to be stable?

选项：

解释：

Given that the equation has a unit root means that the factorization of the characteristic equation must be of the form:

$(z - 1)(z - c) = z^2 - (c + 1)z + c$,

where 0 < | c| < 1

The characteristic equation for the original relationship is

$z^2 - kz - m$

Therefore, it is required that |m| < 1 and

k = (-m + 1) or (1 - m)