hello,everyone,,why is that?

As the number of 9s behind the decimal approaches infinity, the difference between the number and 1 approaches zero.

If x = .999999...... where the ellipses are meant to indicate an infinite number of nines
10x = 9.99999......
Evaluate 10x - x by subtraction of the above:

9.99999999
- .99999999
-----------------
9.0

10x - x = 9x = 9 ===> x = 1

oh , i see

thank you~