Answer:
Seven isn't part of the set of irrational numbers.
Step-by-step explanation:
Start with the smallest set among the choices. The set of all natural numbers, [tex]\mathbb{N}[/tex], starts with [tex]0[/tex] (or [tex]1[/tex], for some people.) A number [tex]n[/tex] is in [tex]\mathbb{N}\!\!\![/tex] (write [tex]n \in \mathbb{N}[/tex]) if and only if [tex](n - 1)[/tex] is in [tex]\mathbb{N}\![/tex]. Conversely, if [tex]n\![/tex] is indeed in [tex]\mathbb{N}\!\!\!\!\![/tex], then [tex](n + 1)[/tex] would also be in [tex]\mathbb{N}\!\!\!\!\!\!\![/tex]. For [tex]7[/tex]:
[tex]1 \in \mathbb{N} \implies 2 \in \mathbb{N}[/tex].
[tex]\vdots[/tex].
[tex]6 \in \mathbb{N} \implies 7 \in \mathbb{N}[/tex].
Therefore, [tex]7[/tex] is indeed in the set of all natural numbers.
Similarly, a number [tex]n[/tex] is in the set of integers, [tex]\mathbb{Z}[/tex], if and only if either [tex](n - 1)[/tex] or [tex](n + 1)[/tex] is (or both are) in [tex]\mathbb{Z}\!\![/tex].
Conversely, if a number [tex]n[/tex] is in [tex]\mathbb{Z}[/tex], then both [tex](n - 1)[/tex] and [tex](n + 1)[/tex] will be in [tex]\mathbb{Z}\![/tex].
It can be shown in a similar iterative way that [tex]7 \in \mathbb{Z}[/tex].
Alternatively, consider the fact that the set of all natural numbers, [tex]\mathbb{N}[/tex], is a subset of the set of all integers, [tex]\mathbb{Z}[/tex]. Therefore, [tex]7 \in \mathbb{N}[/tex] implies that [tex]7 \in \mathbb{Z}[/tex].
A number [tex]m[/tex] is a member of the set of all rational numbers [tex]\mathbb{Q}[/tex] if and only if there exists two integers [tex]p[/tex] and [tex]q[/tex] such that:
[tex]\displaystyle m = \frac{p}{q}[/tex].
[tex]1[/tex] and [tex]7[/tex] are both integers. If [tex]p = 7[/tex] and [tex]q = 1[/tex], then [tex]\displaystyle 7 = \frac{7}{1} = \frac{p}{q}[/tex]. Hence,
Alternatively, note that the set of all integers, [tex]\mathbb{Z}[/tex], is a subset of the set of all rational numbers, [tex]\mathbb{Q}[/tex]. Therefore, the fact that [tex]7 \in \mathbb{Z}[/tex] would imply that [tex]7 \in \mathbb{Q}[/tex].
A number is in the set of all irrational numbers if and only if:
Therefore, the fact that [tex]7[/tex] is a rational number implies that it is not an irrational number.
