Prove there is an irrational between any two rationals

  • Thread starter Quantumpencil
  • Start date
  • Tags
    Irrational
In summary, the conversation discusses the proof that there exists an irrational number between any two rational numbers. It involves using the density of irrationals between any two real numbers and manipulating rational and irrational numbers to reach the desired result.
  • #1
Quantumpencil
96
0

Homework Statement



Prove that there exists an irrational between any two rationals.



Homework Equations





The Attempt at a Solution



How would one do this? So far I've proven there is an irrational between any rational and irrational, any irrational and rational, that there's a rational between any two reals, or a irrational between any two reals in the attempt; I realize that it can be taken as a case of the last two; but I haven't been able to start with just p,q such that p>q, and p and q rational, and arrive at this result. It's pissing me off.

Thanks in advance.
 
Physics news on Phys.org
  • #2
Let p ,q be rationals with p>q

Let e be a positive real. Then for e < |p-q|, q+e is in the open interval (p, q). Due to the density of the irrationals in R (as you pointed out, between any two reals is a rational), there is a positive irrational, call it a, that is less than e. Now take q+a. What can you say about that value?
 
  • #3
Say the two rationals are p and q.
define
x=[(p+q)/2]+[(p-q)/2]r/n
where r is any irrational and n is any integer such that
|r|<n

show
(1/2)(p+q-|p-q|)<x<(1/2)(p+q+|p-q|)
or
|2x-p-q|<|p-q|
and
x is irrational
 
Last edited:

1. What does it mean for a number to be irrational?

An irrational number is a number that cannot be expressed as a ratio of two integers. This means that it cannot be written in the form of a fraction with a finite number of digits. Examples of irrational numbers include pi (π) and the square root of 2 (√2).

2. Why is it important to prove that there is an irrational number between any two rational numbers?

This proof is important because it provides evidence for the existence of irrational numbers and helps to understand the relationship between rational and irrational numbers. It also helps to explain why the real numbers, which include both rational and irrational numbers, are infinitely dense.

3. How can you prove that there is an irrational number between any two rational numbers?

This can be proven using a proof by contradiction. Assume that there is no irrational number between two rational numbers, then show that this assumption leads to a logical contradiction. This contradiction proves that the assumption is false, and therefore there must be an irrational number between any two rational numbers.

4. Can you give an example of an irrational number between two rational numbers?

Yes, let's take the rational numbers 1 and 2. The square root of 2 (√2) is an irrational number that lies between 1 and 2. Its decimal representation is infinite and non-repeating, making it an irrational number.

5. What is the significance of this proof in mathematics?

This proof has significant implications in various fields of mathematics such as calculus, number theory, and geometry. It helps to establish the completeness of the real numbers, which is crucial in the development of many mathematical concepts and theories. It also serves as a foundation for understanding the properties of irrational numbers and their relationship with rational numbers.

Similar threads

  • Calculus and Beyond Homework Help
Replies
8
Views
1K
  • Calculus and Beyond Homework Help
Replies
7
Views
1K
  • Calculus and Beyond Homework Help
Replies
3
Views
1K
  • Calculus and Beyond Homework Help
Replies
7
Views
2K
  • Calculus and Beyond Homework Help
Replies
2
Views
1K
  • Calculus and Beyond Homework Help
Replies
1
Views
2K
  • Calculus and Beyond Homework Help
Replies
5
Views
2K
  • Calculus and Beyond Homework Help
Replies
11
Views
2K
Replies
4
Views
2K
  • Calculus and Beyond Homework Help
Replies
18
Views
4K
Back
Top