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!