0.8999... + ((1 / 9) * 0.8999...) = 0.9999... = 1이라고 할때

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= 0.8999... + /  (1 / 9(0.1111...) * 0.8999...) = 0.0999...

= 0.8999(0.9) + 0.0999(0.1) = 1

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= 0.8999... + (0.1111... * 0.8999...)

= 0.9 + (0.1 * 0.9...)

= 0.9 + 0.09

= (0.99 == 1)가 된다.