# Which sets of numbers are countable?

## Which sets of numbers are countable?

Examples of countable sets include the integers, algebraic numbers, and rational numbers. Georg Cantor showed that the number of real numbers is rigorously larger than a countably infinite set, and the postulate that this number, the so-called “continuum,” is equal to aleph-1 is called the continuum hypothesis.

## What are sets of real numbers?

Common Sets The set of real numbers includes every number, negative and decimal included, that exists on the number line. The set of real numbers is represented by the symbol R . The set of integers includes all whole numbers (positive and negative), including 0 . The set of integers is represented by the symbol Z .

Is the set of real numbers from 0 to 1 countable?

So Set of Real Numbers Between 0 and 1 is Countably Infinite.

### What is countable sets with example?

The basic examples of (finite) countable sets are sets given by a list of their elements: The set of even prime numbers that contains only one element: {2}. The set of prime numbers less than 10: {2,3,5,7}. The set of diagonals in a regular pentagon ABCDE: {AC,AD,BD,BE,CE}.

### Which is not a countable set?

Uncountable is in contrast to countably infinite or countable. For example, the set of real numbers in the interval [0,1] is uncountable. There are a continuum of numbers in that interval, and that is too many to be put in a one-to-one correspondence with the natural numbers.

How do you write a set of real numbers?

“The set of all real numbers x, such that x is greater than −2 and less than or equal to 3.” has domain that consists of all real numbers greater than or equal to zero, because the square root of a negative number is not a real number. We can write the domain of f(x) in set builder notation as, {x | x ≥ 0}.

## What makes a set uncountable?

A set is uncountable if it contains so many elements that they cannot be put in one-to-one correspondence with the set of natural numbers. Uncountable is in contrast to countably infinite or countable. For example, the set of real numbers in the interval [0,1] is uncountable.

## How do you prove something is countable?

We say a set A is countably infinite if N≈A, that is, A has the same cardinality as the natural numbers. We say A is countable if it is finite or countably infinite. In the last two examples, E and S are proper subsets of N, but they have the same cardinality.

Is set of real number countable?

The set of real numbers R is not countable. We will show that the set of reals in the interval (0, 1) is not countable. This proof is called the Cantor diagonalisation argument. Hence it represents an element of the interval (0, 1) which is not in our counting and so we do not have a counting of the reals in (0, 1).

### What are real numbers between 0 and 1?

Hence, there are no whole numbers between 0 and 1. NB: There are in fact an infinite number of real numbers in the interval (0,1) . These consist of the rational numbers which can be represented by pq{p,q}∈Z:q≠0 (such as 12 ) and irrational numbers which cannot be represented by pq{p,q}∈Z:q≠0 (such as 1√2 ).

### How are the real numbers a countable set?

Then we simply extend this to all real numbers and all the whole numbers themselves, and since the real numbers, as demonstrated above, between any two whole numbers is countable, the real numbers are the union of countably many countable sets, and thus the real numbers are countable.

How is a countable set different from an enumerable set?

Not to be confused with (recursively) enumerable sets. In mathematics, a countable set is a set with the same cardinality ( number of elements) as some subset of the set of natural numbers. A countable set is either a finite set or a countably infinite set.

## Which is the countable union of natural numbers?

Theorem: The set of all finite-length sequences of natural numbers is countable. This set is the union of the length-1 sequences, the length-2 sequences, the length-3 sequences, each of which is a countable set (finite Cartesian product). So we are talking about a countable union of countable sets, which is countable by the previous theorem.

## Which is the countable set of all rational numbers?

Theorem: Z (the set of all integers) and Q (the set of all rational numbers) are countable. In a similar manner, the set of algebraic numbers is countable. These facts follow easily from a result that many individuals find non-intuitive. Theorem: Any finite union of countable sets is countable.