In mathematics, 0.999… (also denoted or ) is a recurring decimal exactly equal to 1. In other words, the symbols '0.999…' and '1' represent the same real number. Mathematicians have formulated numerous proofs of this identity, which vary as to their level of rigor, preferred development of the real numbers, background assumptions, historical context, and target audience.

http://en.wikipedia.org/wiki/0.999...

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