Rational numbers - bounded subset with no least upper bound

In summary, a bounded subset of Q that has no least upper bound in Q must contain numbers that are not rational, such as irrational numbers.
  • #1
ciarax
6
0

Homework Statement




Give an example of a bounded subset of Q which has no least upper
bound in Q. Explain why your answer has this property.


Homework Equations





The Attempt at a Solution



[1/8, 1/4, 3/8, 1/2, 5/8, 3/4...infinity]
is this correct?
 
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  • #2
ciarax said:

Homework Statement




Give an example of a bounded subset of Q which has no least upper
bound in Q. Explain why your answer has this property.


Homework Equations





The Attempt at a Solution



[1/8, 1/4, 3/8, 1/2, 5/8, 3/4...infinity]
is this correct?

No. Hint: What kind of numbers are missing from Q? Find a bounded set that has one of them for its lub.
 
  • #3
ciarax said:
Give an example of a bounded subset of Q which has no least upper
bound in Q. Explain why your answer has this property.

[1/8, 1/4, 3/8, 1/2, 5/8, 3/4...infinity]
Your set appears to be integer multiples of 1/8. This set is not bounded, so doesn't qualify as an example in this problem.
 

What are rational numbers?

Rational numbers are numbers that can be expressed as a ratio of two integers, where the denominator is not equal to zero. They can be written in the form of a/b, where a and b are integers.

What is a bounded subset?

A bounded subset is a set of numbers that has a finite upper and lower limit. This means that all the numbers in the subset fall within a specific range.

What does it mean for a bounded subset to have no least upper bound?

This means that the subset does not have a maximum value. While there is an upper limit to the numbers in the subset, there is no single number that is greater than all the others.

Can a rational number be a bounded subset with no least upper bound?

Yes, a rational number can be a bounded subset with no least upper bound. This can happen when the subset contains numbers that are infinitely close to the upper limit, but not equal to it.

What are some examples of rational numbers that are bounded subsets with no least upper bound?

One example is the set of rational numbers between 0 and 1, where the upper limit is 1 but there is no rational number that is greater than all the others. Another example is the set of rational numbers between 1 and 2, where 2 is the upper limit but there is no single rational number that is greater than all the others.

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