0.9 infinite loop = 1

To prove this point:

The method 1 is the simplest and clearest.

Let x = 0.99...；; Then10x = 9.99 ...; Then 10X-X=9 can get X= 1.

Similarly, 9.99...= 10

Method 2 introduces the concept of limit.

The concept of limit appears in high school mathematics.

0.9999……

=0.9+0.09+0.009+……

= 0.9 * (1+0.1+0.01+0.001+...) geometric series sum.

= 0.9 * (1-0.1n)/(1-0.1), and n tends to infinity.

=0.9* 1/0.9

= 1

Similarly, 9.99...= 10