High Quality Content by WIKIPEDIA articles! In mathematics, the repeating decimal 0.999... (which may also be written as 0.9, , 0.(9), or as "0." followed by any number of 9s in the repeating decimal) denotes a real number that can be shown to be the number one. In other words, the symbols 0.999... and 1 represent the same number. Proofs of this equality have been formulated with varying degrees of mathematical rigour, taking into account preferred development of the real numbers, background assumptions, historical context, and target audience.