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I Proof: 0.9999 does not equal 1

  1. Nov 22, 2017 #1
    Or rather counter proof.
    They said x=0.999...
    10x=9.999....
    9x=9.999....-x
    9x=9
    x=1
    but this is obviously wrong, you can't substract infinity from infinity unless you consider infinity a number and if so then you would get 8.99...1 and not 9. either way 0.999....= 1 is wrong. and is not different than saying (0.999...) +x=1.99...8 you can't add an infine amount of nines to an infinite amount of nines or subtract. if you could then you would consider infinity as a number and in that case the proof is also wrong
     
  2. jcsd
  3. Nov 22, 2017 #2

    DrClaude

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    Staff: Mentor

    This subject has been discussed many times on PhysicsForums. Please do a search of the forum or look at the "Similar Discussions" links below.

    Yes, 0.999... = 1.

    Thread closed.
     
  4. Nov 22, 2017 #3

    Mark44

    Staff: Mentor

    We are not subtracting infinity from infinity here. The subtraction is 9.999... - 0.999..., with each number having an infinte number of 9 digits to the right of the decimal point. The result is 9.000..., with an infinite number of 0 digits to the right of the decimal point.
    As DrClaude said, this has been discussed many times here at PF.
     
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