Math Question from PrepSwift Video "Operations with Expressions"

3 questions from his Prepswift videos “simplifying algebraic expressions II” AND “Operations with Expressions”…

1… I am not understanding the concept of how Greg is determining that “X+1/X+1 = 1 usually, except x can not equal -1”. His reasoning for some reason is not clicking and I have rewatched the video.

2… Also, I am not understanding how he determines when x can NOT equal certain numbers.
---- For e.g. from his video he had “2x+3/4-5x” and said that x can not equal 0 or 4/5…
---- How did he choose these/know how to determine if x cannot equal these numbers? I am just not understanding the concept.

3… From his video “simplifying algebraic expressions II”, I am not understanding when/how does he determine whether the answer needs to be in the absolute value brackets or not and the reasoning behind how he “tests” it out.

Thanks in advance!

What happens when x = -1?

I think your second expression is wrong.