z-transform of a sequence [EXL]

http://youtu.be/i2_8p_N8urs?t=6m12s

Poles

The real part of the pole :

•  > 0  determines whether something grows exponentially
• = 0 ,stays constant
• < 0 ,decreases exponentially

The imaginary part of the pole tells me whether there is an isolation in a time signal.