Determining if Numbers are in the Cantor Set

In summary, the two numbers 509/729 and 511/729 are being examined to determine if they are in the Cantor set. The first number, 509/729, in base 3 is 0.200212, which cannot be expanded using only 0 and 2. Therefore, it is not part of the Cantor set. The second number, 511/729, in base 3 is 0.200221, which can be expanded using only 0 and 2, making it part of the Cantor set. Additionally, the endpoint .02002213 of an open interval in the Cantor set is also examined and determined to be part of the set.
  • #1
spitz
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Homework Statement



I have two numbers: 509/729 and 511/729. I want to determine if they are in the Cantor set.

The Attempt at a Solution



I have:

509/729 in base 3 is: 0.200212

So this is not part of the cantor set because it can't be expanded in base 3 using only 0 and 2.

---------------------

511/729 in base 3 is: 0.200221

For this one, am I correct in saying that 0.200221 = 0.200220222...

So, it can be expanded using only 0 and 2, and so is part of the cantor set?
 
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  • #2
Indeed, both look good to me!
 
  • #3
Since we form the Cantor set by removing open intervals, the endpoins of those intervals remain in the Cantor set. .02002213 is such an endpoint.
 

1. What is the Cantor Set?

The Cantor Set is a mathematical set that is constructed by repeatedly removing the middle third of a line segment. The resulting set is a fractal with a unique structure that has both a finite and infinite number of points.

2. How do you determine if a number is in the Cantor Set?

A number is considered to be in the Cantor Set if, after repeatedly dividing it by 3 and removing the middle third, it results in a non-zero remainder. If the remainder is always zero, then the number is not in the Cantor Set.

3. Is every number on the real number line in the Cantor Set?

No, not every number on the real number line is in the Cantor Set. In fact, the Cantor Set is a perfect example of a set that is both infinite and uncountable, yet still has a measure of zero. This means that although there are an infinite number of points in the Cantor Set, they are so sparse that they do not take up any space on the real number line.

4. Can you use a formula to determine if a number is in the Cantor Set?

Yes, there is a formula called the Cantor Set function that can be used to determine if a number is in the Cantor Set. This function takes in a number and repeatedly divides it by 3 while checking for non-zero remainders. If the number eventually reaches 0, then it is in the Cantor Set. If not, then it is not in the Cantor Set.

5. What is the significance of the Cantor Set in mathematics?

The Cantor Set is significant in mathematics because it is one of the first and most well-known examples of a fractal, which is a geometric pattern that repeats on different scales. It also has applications in number theory and topology, and has led to the development of other important mathematical concepts such as the Cantor function and the Cantor space.

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