quote:
10x - x = 9.99999999 - 0.999999999
9x = 8.9999999991
How did you get 8.9999999991

Did you notice the "..." which should mean infinite repetition (as in limit tends to)...?
quote:
(if i may add: duh)
Not yet! [|)]
And for Squeek's one, I think you cannot that easily cancel (a2-ab); it has a special value... [|)]