Proving the Empty Intersection of Intervals using Natural Numbers

In summary, the conversation discusses proving that the intersection of the intervals (0, 1/n) for n=0 to infinity is empty. The attempted solution states that the intersection is empty because 0 is not included in the intervals and as x approaches 0, there will always be a natural number k such that 1/k < x. However, if the intervals were changed to [0, 1/n], the intersection would not be empty. The conversation also suggests further clarifying the proof by showing that for any x > 0, there exists a natural number k such that 1/k < x.
  • #1
cragar
2,552
3

Homework Statement


Prove that [itex] \bigcap_{n=0}^{\inf} (0,\frac{1}{n})=\emptyset [/itex]

The Attempt at a Solution


since 0 is not included in our interval. eventually I will get to
(0,0) because I could pick a real as close to zero as I wanted and there would be a natural such that [itex] \frac{1}{n}<y [/itex] therefore this intersection is empty.
but if my orginal intersection was [0,1/n] then this would not be empty.
 
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  • #2
You have the right idea, and you're correct that if (0,1/n) was replaced by [0,1/n], the intersection would not be empty. It would contain exactly one point: 0.

You could word your proof a bit precisely as follows:

Suppose the intersection is non-empty. Then there exists some x in the intersection:

[tex]x \in \bigcap_{n=1}^{\infty} (0, 1/n)[/tex]

Since x is in the intersection, it means that x must be in every interval of the form (0, 1/n), and this is impossible because...
 
  • #3
ok thanks for the input
 
  • #4
you might want to show that if x > 0, there exists k in N with 1/k < x, first.
 

1. What does it mean to "prove intersection is empty"?

Proving intersection is empty means showing that there are no elements or objects that are common or shared between two sets. In other words, the intersection of two sets is the empty set, indicating that there is no overlap between the two sets.

2. How do you prove that the intersection of two sets is empty?

To prove that the intersection of two sets is empty, you can use a direct proof or a proof by contradiction. In a direct proof, you would show that for any element in one set, it does not exist in the other set. In a proof by contradiction, you would assume that there is an element in both sets and then show that it leads to a contradiction, thereby proving that the intersection is empty.

3. Why is proving intersection is empty important in mathematics?

Proving intersection is empty is important in mathematics because it allows us to determine if two sets are completely separate and have no common elements. This is useful in various areas of mathematics, such as set theory, geometry, and algebra, where we need to determine relationships between sets.

4. Can you give an example of proving intersection is empty?

Yes, for example, let's say we have two sets A = {1, 2, 3} and B = {4, 5, 6}. To prove that their intersection is empty, we can use a direct proof by showing that for any element in set A, it does not exist in set B. In this case, we can say that 1, 2, and 3 do not exist in set B, thus proving that the intersection is empty.

5. Are there any other methods for proving intersection is empty?

Yes, apart from direct proof and proof by contradiction, there are other methods for proving intersection is empty, such as using Venn diagrams, set complements, and the pigeonhole principle. Each method may be more suitable for different types of sets and situations.

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