# Second order system with additional pole

Why is it that a second order system with an additional pole or zero can be approximated into the general second order system for analysis?

This was asked during our lecture and I am still looking for the answer.

In my reading I've only learned that when an additional pole or zero is added to the system, the step response of this system starts to resemble the step response of the original system. I am not sure if this is the answer to the question.