Proving Square is an Infinite Set

In summary, the problem is asking to prove that the set of square numbers is infinite, meaning that there is an injection from the set of square numbers to itself that is not a surjection. The attempt at a solution involves showing an injection by defining a function that maps each number to its square, but this does not work for all numbers, thus proving that it is not a surjection. The set in question is {x ∈ N|∃y : N. x = y^2}, which is the set of square numbers.
  • #1
amiv4
25
0

Homework Statement



Prove that Square = {x ∈ N|∃y : N. x = y^2} is an infinite set.


Homework Equations



Definition 0.1. A set A is infinite if there is an injection f : A → A that is not also a surjection.

The Attempt at a Solution



I get how to show that there is an injection, but i don't get how to show that it is also not a surjection
 
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  • #2
What injection are you looking at?
 
  • #3
to prove the injection i thought u could do something like this

f(x) = f(y) for arbitrary x and y in N, then x^2 = y^2 and so x = y. and that proves an injection
 
  • #4
amiv4 said:

Homework Statement



Prove that Square = {x ∈ N|∃y : N. x = y^2} is an infinite set.
What is the above supposed to be saying?
amiv4 said:

Homework Equations



Definition 0.1. A set A is infinite if there is an injection f : A → A that is not also a surjection.

The Attempt at a Solution



I get how to show that there is an injection, but i don't get how to show that it is also not a surjection
 
  • #5
would it be that like 0 maps to 0, 1 to 1, 2 to 4, 3 to 9... so that shows injection but then like 5 doesn't map back to anything
 
  • #6
Except you're supposed to have a map that goes from the set of squares to the set of squares. But the function that you're looking at will still work
 
  • #7
so would it be like 4 mapped to 16 is an injection but if you go the other way 16 doesn't map back to 4 and that is why it isn't a surjection
 
  • #8
What set is this? {x ∈ N|∃y : N. x = y^2}

Some characters are rendering as empty boxes.
 
  • #9
it is bascially the set of square numbers
 

1. How do you define an infinite set?

An infinite set is a set that has an uncountable number of elements. This means that there is no limit to the number of elements in the set and it cannot be exhausted by counting.

2. What is a square in terms of mathematics?

In mathematics, a square is a geometric shape with four equal sides and four equal angles, forming a right angle at each corner. It is also known as a regular quadrilateral.

3. Can a square be considered an infinite set?

Yes, a square can be considered an infinite set. In terms of set theory, a square can be defined as an infinite set of points that are equidistant from a central point.

4. How can you prove that a square is an infinite set?

A square can be proved to be an infinite set by showing that it has an uncountable number of elements. This can be done by using the Cantor diagonal argument, which states that any attempt to count the elements of an infinite set will always result in a larger uncountable set.

5. Are there any other methods to prove that a square is an infinite set?

Yes, there are other methods to prove that a square is an infinite set. One method is by using the concept of one-to-one correspondence, where each element in the set can be paired with a unique element in the set of natural numbers. Another method is by using the concept of limit in calculus, where the perimeter of a square can be shown to approach infinity as the length of its sides increases.

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