How to prove √X is irrational number

Click For Summary

Discussion Overview

The discussion revolves around the proof of whether the square root of a number \( \sqrt{X} \) is irrational, particularly focusing on the conditions when \( X \) is an even or odd number. Participants explore various approaches and challenges related to this topic.

Discussion Character

  • Exploratory
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants suggest that proving \( \sqrt{X} \) is irrational is straightforward when \( X \) is even, but they express uncertainty about the case when \( X \) is odd.
  • There is confusion regarding whether \( \sqrt{4} \) is irrational, with multiple participants questioning this claim.
  • One participant proposes that \( \sqrt{x} \) is irrational if and only if \( x \) is not a perfect square, although this assertion is met with a request for proof.
  • A reference to the Fundamental Theorem of Arithmetic is made, suggesting an approach involving the assumption \( p^2/q^2=x \) with \( \text{gcd}(p,q)=1 \) to explore divisibility.
  • Clarification is provided on the term "gcd," which stands for greatest common divisor, and its relevance to the proof process.
  • One participant recommends looking at existing proofs, specifically for \( \sqrt{2} \), and adapting them for other cases, while noting that the concept of "even" may not apply universally outside of specific examples.
  • Links to Wikipedia entries are shared for further exploration of square roots and the history of irrational numbers.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the proof of \( \sqrt{X} \) being irrational, particularly for odd values of \( X \). Multiple competing views and uncertainties remain regarding the definitions and conditions involved.

Contextual Notes

Limitations include the lack of a clear proof for the case when \( X \) is odd, as well as unresolved questions about the implications of the Fundamental Theorem of Arithmetic in this context.

SOHAWONG
Messages
16
Reaction score
0
when X is even number,it's easy to prove
but how about the condition which X is odd number?
I have no idea of this
 
Mathematics news on Phys.org
\sqrt{4} is irrational?
 
Hurkyl said:
\sqrt{4} is irrational?
no,i may add despite 1,4,9,16,25...etc
 
So in other words...

\sqrt{x} is irrational iff x=/=n^2 for n belonging to the integer set.
 
Char. Limit said:
So in other words...

\sqrt{x} is irrational iff x=/=n^2 for n belonging to the integer set.
yes, but how to prove?:confused:
 
Fundamental theorem of arithmetic. Assume p^2/q^2=x with gcd(p,q)=1, and see what has to divide what.
 
Tinyboss said:
Fundamental theorem of arithmetic. Assume p^2/q^2=x with gcd(p,q)=1, and see what has to divide what.

what does gcd mean?
 
Greatest common divisor. If gcd(p,q)=1, it means the fraction p/q is in lowest terms.

Look at the proof for sqrt(2), and adapt it. Remember that "even" just means "is divisible by 2", so that if you're checking a number other than 2, you won't be thinking about "even" anymore.
 

Similar threads

  • · Replies 9 ·
Replies
9
Views
2K
  • · Replies 10 ·
Replies
10
Views
3K
  • · Replies 28 ·
Replies
28
Views
3K
  • · Replies 7 ·
Replies
7
Views
2K
Replies
4
Views
3K
Replies
16
Views
3K
  • · Replies 7 ·
Replies
7
Views
3K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 19 ·
Replies
19
Views
4K