I am trying to study time series without a great math background and I came across the next problem:

When checking for stationarity I check the roots, and if they are not on the unit circle, then it confirms the ts is stationary.

My question might be pretty basic: when I get the roots, I am getting scalars, whereas in my mind to be inside/outside unit circle I need coordinates... How do I know if a scalar is inside/outside the unit circle?

And my last question is, I always read "roots are not on the unit circle".

"on" means "inside", right? and if so... Is it the same as saying "roots are outside the unit circle"?