AP Calculus AB Clarification Request

Hello,

I've just finished the "Connecting limits at infinity and horizontal asymptotes" section in the first unit of AP Calculus AB and I ran into a common misunderstanding that was barely addressed in the videos for "limits at infinity of quotients with square roots." I don't want others to get confused about the same thing that I was.

The misunderstanding is difficult to explain, but it comes up when limits, as x approaches negative infinity, have odd powers you have to divide by to solve them. I know that it's addressed in the video titles and question explanations, but neither actually explain why you have to change the sign. I've linked the youtube resources I used to figure this out below for anyone stuck on the lesson and to better explain the exact issue.

https://www.youtube.com/watch?v=UBP1GxYxHLY 

https://www.youtube.com/watch?v=JCywS6htWTQ 

Thanks for reading!