In mathematics, the repeating decimal 0.999... (sometimes written with more or fewer 9s before the final ellipsis, for example as 0.9..., or in a variety of other variants such as 0.9, 0.
0,(9) или 0,999… (formula_1) («ноль и девять в периоде») — периодическая десятичная дробь, представляющая число 1.