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#1 Puzzles and Games » Is this True? » 2006-04-03 22:19:27

MatthewMc
Replies: 6

Is this really true?
The conjecture is that 0.9 recurring (i.e. 0.9999....9) is actually equal to 1
(For this exercise I will use the notation 0.999... as notation for 0.9 recurring,
the correct way would be to put a little dot above the 9)

  • Let X = 0.999... 
   
• Then 10X = 9.999... 
 
Subtract X from each side to give us:
• 9X = 9.999... - X
 
but we know that X is 0.999..., so: 
• 9X = 9.999... - 0.999...
or: • 9X = 9
   
Divide both sides by 9:
• X = 1 
   
But hang on a moment I thought we said X was equal to 0.999...

Yes, it does, but from our calculations X is also equal to one. So:
• X = 0.999... = 1 
   
• Therefore 0.999... = 1 
   
Does anyone disagree with this? Let me know using the math is fun forum.

No, this is not true, properly following the initial equation set out we find that.

X=.999
10X=9.99

Yet,
9X=8.991, and not in fact 9.999, so following through X=8.991/9 being .999 so X conforms to the expected solution.

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