In fact, 0.999999999 (there are infinitely many 9s) and 1 are completely equal!
Before proving, we must first understand a mathematical law.
0.99999999999 ... and 0.999...999 are two completely different numbers in mathematics. The former means that the number of 9 is infinite; The latter means that the number of 9 is limited, so it is generally necessary to indicate the number of 9 after it.
Therefore, 0.999999999 ... means that the number of 9 is infinite, which must be clear first. Then we can use the knowledge of geometric series to prove the above conclusion. The proof process is as follows:
0.999999999 ...= 0.9+0.09+0.009+0.0009+...= 0.9 *( 1-0. 1N)/( 1-0. 1)
Therefore, 0.99999999 = 1 is effective.