well, by following the order of operations, PEMDAS, you do addition BEFORE subtraction….

1-(1+1)-1=
1–2–1=(one minus two equals negative one, minus one)
-1–1=
(-1)-1 …(multiply them together because you multiply a number beside parenthesis by the number in the parenthesis)= 1

If you DONT follow the math rules, then you have 0+0=0….

NOTHING in math can EVER be two different things when the math is done correctly.