Friday, October 4, 2019

elementary number theory - How to express 0.999999... recurring as a fraction without equaling 1





I was wondering is there any way to express 0.999999 recurring as an actual fraction without equaling 1? Because I tried to convert it into a fraction following the rules for normal recurring decimals like this:



n=0.999˙910n=9.999˙9n=0.999˙99n=9



But as you can see the result is 9/9 which ultimately is equal to 1 . And I've even tried calculating it other ways like this:




\begin{align}1/3&=0.333\dot3\\2/3&=0.666\dot6\\\therefore3/3&=0.999\dot9\end{align}



But it always ends up telling me that 0.9999999... = 1. Is there any mistake in my logic? And I also realized this applied to other recurring decimals ending in 9. E.g: 0.5999999...=5.4/9 = 0.6 . So is there a way to write 0.999999... as a fraction so you can differentiate it from 1?


Answer



As you have proven by yourself,
0.999999999999999999999\dot9 = 1.
There are no (big) logical mistakes in your post.




Because 0.99\dots is equal to 1, it also cannot be another fraction.


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