Question

For what value of x is the rational expression below undefined? 1-x x+1

Answer 1

If 1-x/x+1 is undefined then the bottom number must be 0
set
x+1=0
x=-1

Answer 2

Hm 1-x=0 and x+1=0 so we need to make them bothe equal zero so we just flip both ones and we should get when 1-x=0, x=1 and when x+1=0, x=-1