Drexel dragonThe Math ForumDonate to the Math Forum

Ask Dr. Math - Questions and Answers from our Archives
_____________________________________________
Associated Topics || Dr. Math Home || Search Dr. Math
_____________________________________________

Possible Proof That 1 + 1 Does Not Equal 2


Date: 04/19/2001 at 01:57:44
From: Desmond Leung
Subject: A possible proof for 1+1 not equal 2

A buddy of mine told me how to prove that 1 + 1 does not equal 2, and 
some say he was correct. I just want verification.

It goes something like this:

     1 = 1/3 + 1/3 + 1/3
     1 = 0.333... + 0.333... + 0.333...     (... means repeated)
     1 = 0.999...

normally

     lim    (1)^n = 1
     n->inf

but

     lim    (0.999...)^n = 0
     n->inf

therefore

     lim    [(0.999...)^n + (0.999...)^n] = 0
     n->inf

which does not equal 2.

Would this work?


Date: 04/19/2001 at 14:27:47
From: Doctor TWE
Subject: Re: A possible proof for 1+1 not equal 2

Hi and thanks for writing to Dr. Math.

Here's the problem with this "proof."

     lim   (0.999...9)^n = 0
     n->oo

is true only if there is a *finite* number of 9's in the value in 
parentheses. With an infinite number of 9's, the expression becomes:

             oo
     lim   [sum(9/10^k)]^n
     n->oo  k=1

and we cannot conclude that this expression goes to zero.

For more information on false "proofs" of this sort, see the Dr. Math 
FAQ at:

   http://mathforum.org/dr.math/faq/faq.false.proof.html   

I hope this helps. If you have any more questions, write back.

- Doctor TWE, The Math Forum
  http://mathforum.org/dr.math/   
    
Associated Topics:
High School About Math
High School Calculus
High School Sequences, Series

Search the Dr. Math Library:


Find items containing (put spaces between keywords):
 
Click only once for faster results:

[ Choose "whole words" when searching for a word like age.]

all keywords, in any order at least one, that exact phrase
parts of words whole words

Submit your own question to Dr. Math

[Privacy Policy] [Terms of Use]

_____________________________________
Math Forum Home || Math Library || Quick Reference || Math Forum Search
_____________________________________

Ask Dr. MathTM
© 1994-2013 The Math Forum
http://mathforum.org/dr.math/