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## Homework Statement

[itex]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}}[/itex]

where [itex]A = (6-z^{-1})[/itex] is evaluated at [itex]z^{-1}=-2[/itex].

## Homework Equations

Partial fraction expansion.

## The Attempt at a Solution

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