Partial Fraction Expansion (Inverse Z-Transform)

[ElfenKiller]

Homework Statement

$H(z) = \frac{6-z^{-1}}{1+0.5z^{-1}} + \frac{2}{1-0.4z^{-1}} = k + \frac{A}{1+0.5z^{-1}} + \frac{2}{1-0.4z^{-1}}$

where $A = (6-z^{-1})$ is evaluated at $z^{-1}=-2$.

Homework Equations

Partial fraction expansion.

The Attempt at a Solution

Why is $z^{-1}$ set equal to -2? I thought normally you use the terms in the denominators for $z^{-1}$ ...

 

[vela]

What do you mean by "use the terms in the denominator for $z^{-1}$"? Use them how?

 

[ElfenKiller]

What do you mean by "use the terms in the denominator for $z^{-1}$"? Use them how?

Like here: http://dspcan.homestead.com/files/Ztran/zinvpart.htm"