1 is by definition 0.999999999 9?

  • Context: High School 
  • Thread starter Thread starter adarpodracir
  • Start date Start date
  • Tags Tags
    Definition
Click For Summary

Discussion Overview

The discussion revolves around the mathematical statement that 0.999... is equal to 1. Participants explore the implications of this equality, the reasoning behind it, and potential objections to the concept. The scope includes mathematical reasoning and conceptual clarification.

Discussion Character

  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant asserts that 0.999... equals 1, explaining it as an infinite sum of a geometric series that converges to 1.
  • The same participant argues that there is no positive distance between 0.999... and 1, suggesting they represent the same number.
  • Concerns are raised about the existence of two different expressions for the same number, which the participant addresses by comparing it to other equivalent expressions.
  • Another participant points out that the original question posed may differ from the title, indicating a potential misunderstanding.
  • A reference to an existing thread is made, suggesting that the topic has been discussed previously.

Areas of Agreement / Disagreement

Participants do not reach a consensus, as some support the equality of 0.999... and 1, while others raise questions and concerns about the implications of this statement.

Contextual Notes

Some arguments depend on the definitions of numbers and the properties of the real number system, particularly regarding the concept of infinitesimals and convergence of series.

adarpodracir
Messages
5
Reaction score
0
Hi there,

I have a question regarding this statement:

35jvtvt.png


My question is whether we can say so...

Thank you very much!
 
Mathematics news on Phys.org
OP, the answer is that .999... = 1. It's an equality. They're two expressions that represent the same number.

The reason this is so is that .999... is defined as the infinite sum

9/10 + 9/100 + 9/1000 + ...

This is a geometric series whose sum is 1. This is proven in first-year calculus.

Another way to see it is that there's no distance between the number denoted by .999... and the number denoted by 1. That is, suppose you say, well, .999... is 1/zillion away from1. But I'll just point out that if you take enough 9's, you'll eventually get WITHIN 1/zillion of 1.

So if there's no conceivable positive difference between .999... and 1, then they must represent the same number.

Possible conceptual objections to this reasoning are things like:

* "But how can you have two different expressions for the same number?" Easy. 4 and 2 + 2 are two different expressions for the same number. It happens all the time.

* There must be an "infinitesimal" difference between 1 and .999..." In the standard real number system, there are no infinitesimals. A distance is either zero or positive. Since there's no positive distance between .999... and 1, the distance between them is zero and they're the same number.

Hope this helps. There are discussions of this topic all over the net.
 
Last edited:
There is already a thread about this. Please visit the Frequently Asked Questions subforum.
 
Do you realize the question you ask in your post and the question you ask in the title are quite different?
 
Please read this: https://www.physicsforums.com/showthread.php?t=507001
 
Last edited by a moderator:
Many thanks to all of you for reply. Everything is clear now.
 

Similar threads

  • · Replies 14 ·
Replies
14
Views
2K
  • · Replies 10 ·
Replies
10
Views
2K
  • · Replies 13 ·
Replies
13
Views
3K
  • · Replies 44 ·
2
Replies
44
Views
5K
  • · Replies 1 ·
Replies
1
Views
2K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 22 ·
Replies
22
Views
3K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 13 ·
Replies
13
Views
2K
  • · Replies 7 ·
Replies
7
Views
2K