Set Theory : Natural Numbers, Integers, and Real Numbers

Study concepts, example questions & explanations for Set Theory

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Example Questions

Example Question #1 : Natural Numbers, Integers, And Real Numbers

Are the sets \(\displaystyle T\) and \(\displaystyle S\) equal?

\(\displaystyle \\T=\begin{Bmatrix} x|x\ \epsilon\ \mathbb{Z} \end{Bmatrix} \\S=\begin{Bmatrix} 2n|n\ \epsilon\ \mathbb{Z} \end{Bmatrix}\)

 

Possible Answers:

\(\displaystyle T\neq S\)

\(\displaystyle T= S, x< 0\)

\(\displaystyle T= S, x\geq0\)

\(\displaystyle T= S\)

\(\displaystyle T= S, x>0\)

Correct answer:

\(\displaystyle T\neq S\)

Explanation:

To determine if two sets are equal to each other it must be proven that each set contains the same elements.

Recall the following terminology,

\(\displaystyle \\\mathbb{Z}=\text{Integers}{\begin{Bmatrix} ...,-2,-1,0,1,2,... \end{Bmatrix}} \\\mathbb{R}=\text{Reals} \\\mathbb{N}=\text{Naturals} {\begin{Bmatrix} 0,1,2,... \end{Bmatrix}}\)

Now, identify the elements in each set.

\(\displaystyle \\T=\begin{Bmatrix} x|x\ \epsilon\ \mathbb{Z} \end{Bmatrix}\)

This means all integers are elements of \(\displaystyle T\).

Let \(\displaystyle x=3\),

\(\displaystyle \\S=\begin{Bmatrix} 2n|n\ \epsilon\ \mathbb{Z} \end{Bmatrix}\)

\(\displaystyle S\) is the value \(\displaystyle 2n\) for all integers.

Therefore if \(\displaystyle n=3\) the element in \(\displaystyle S\) is,

\(\displaystyle 2(n)=2(3)=6\)

This means that all elements in \(\displaystyle S\) will be divisible by two and thus be an even number therefore, 3 will never be an element in \(\displaystyle S\).

Thus, it is concluded that

\(\displaystyle T\neq S\) 

Example Question #11 : Set Theory

Are the sets \(\displaystyle T\) and \(\displaystyle S\) equal?

\(\displaystyle \\T=\begin{Bmatrix} x|x\ \epsilon\ \mathbb{Z} \end{Bmatrix} \\S=\begin{Bmatrix} 1+n|n\ \epsilon\ \mathbb{Z} \end{Bmatrix}\)

Possible Answers:

\(\displaystyle T\neq S\)

\(\displaystyle T= S, x>0\)

\(\displaystyle T= S, x< 0\)

\(\displaystyle T=S\)

\(\displaystyle T\neq S, x\geq0\)

Correct answer:

\(\displaystyle T=S\)

Explanation:

To determine if two sets are equal to each other it must be proven that each set contains the same elements.

Recall the following terminology,

\(\displaystyle \\\mathbb{Z}=\text{Integers}{\begin{Bmatrix} ...,-2,-1,0,1,2,... \end{Bmatrix}} \\\mathbb{R}=\text{Reals} \\\mathbb{N}=\text{Naturals} {\begin{Bmatrix} 0,1,2,... \end{Bmatrix}}\)

Now, identify the elements in each set.

\(\displaystyle \\T=\begin{Bmatrix} x|x\ \epsilon\ \mathbb{Z} \end{Bmatrix}\)

This means all integers are elements of \(\displaystyle T\).

Let \(\displaystyle x=3\),

\(\displaystyle \\S=\begin{Bmatrix} 1+n|n\ \epsilon\ \mathbb{Z} \end{Bmatrix}\)

\(\displaystyle S\) is the value \(\displaystyle 1+n\) for all integers.

Therefore if \(\displaystyle n=3\) the element in \(\displaystyle S\) is,

\(\displaystyle 1+n=1+3=4\)

Since four also belongs to \(\displaystyle \mathbb{Z}\) this means that all elements in \(\displaystyle S\) will be the same as those in \(\displaystyle T\)

Thus, it is concluded that

\(\displaystyle T=S\) 

Example Question #3 : Natural Numbers, Integers, And Real Numbers

What is the correct expression of the relationships between the sets comprised of natural numbers, real numbers, and integers?

Possible Answers:

\(\displaystyle \mathbb{N}\subseteq\mathbb{Z}=\mathbb{R}\)

\(\displaystyle \mathbb{N}=\mathbb{Z}\subseteq \mathbb{R}\)

\(\displaystyle \mathbb{Z}\subseteq\mathbb{N}\subseteq \mathbb{R}\)

\(\displaystyle \mathbb{R}\subseteq\mathbb{Z}\subseteq \mathbb{N}\)

\(\displaystyle \mathbb{N}\subseteq\mathbb{Z}\subseteq \mathbb{R}\)

Correct answer:

\(\displaystyle \mathbb{N}\subseteq\mathbb{Z}\subseteq \mathbb{R}\)

Explanation:

The natural numbers are defined as \(\displaystyle \mathbb{N}=\left \{ 0,1,2,3,...\right \}\), the integers are defined as \(\displaystyle \mathbb{Z}=\left \{ ...-3,-2,-1,0,1,2,3,...\right \}\), and the real numbers (\(\displaystyle \mathbb{R}\)) are defined as the set of all non-complex numbers. As such, \(\displaystyle \mathbb{N}\) is a subset of \(\displaystyle \mathbb{Z}\), and \(\displaystyle \mathbb{Z}\) is a subset of \(\displaystyle \mathbb{R}\).

 

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