Theory of Positive Integers : Theory of Positive Integers

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Example Questions

Example Question #1 : Sets

Let 

\displaystyle S:\begin{Bmatrix} -10,-8,-6,-4,-2,0,2,4 \end{Bmatrix}

if \displaystyle B is some condition of \displaystyle x such that it can be described as \displaystyle \begin{Bmatrix} x\ \epsilon\ S: p(x) \end{Bmatrix} what is \displaystyle p(x) when \displaystyle B=\begin{Bmatrix} 2,4 \end{Bmatrix}?

Possible Answers:

\displaystyle B=\begin{Bmatrix} x\ \epsilon\ S: x< 0 \end{Bmatrix}

\displaystyle B=\begin{Bmatrix} x\ \epsilon\ S: x\geq0 \end{Bmatrix}

\displaystyle B=\begin{Bmatrix} x\ \epsilon\ S: x>0 \end{Bmatrix}

None of the answers

\displaystyle B=\begin{Bmatrix} x\ \epsilon\ S: x\leq0 \end{Bmatrix}

Correct answer:

\displaystyle B=\begin{Bmatrix} x\ \epsilon\ S: x>0 \end{Bmatrix}

Explanation:

First, identify what is given.

\displaystyle S:\begin{Bmatrix} -10,-8,-6,-4,-2,0,2,4 \end{Bmatrix}

\displaystyle B=\begin{Bmatrix} 2,4 \end{Bmatrix}

and \displaystyle B can be described in the following format

\displaystyle B=\begin{Bmatrix} x\ \epsilon\ S: p(x) \end{Bmatrix}

Since \displaystyle B contains the elements in \displaystyle S that are greater than zero, \displaystyle p(x) can be written as follows.

\displaystyle B=\begin{Bmatrix} x\ \epsilon\ S: x>0 \end{Bmatrix}

Example Question #2 : Sets

Let 

\displaystyle S:\begin{Bmatrix} -6,-4,-2,0,2,4 \end{Bmatrix}

if \displaystyle B is some condition of \displaystyle x such that it can be described as \displaystyle \begin{Bmatrix} x\ \epsilon\ S: p(x) \end{Bmatrix} what is \displaystyle p(x) when \displaystyle B=\begin{Bmatrix} -6,-4,-2,0 \end{Bmatrix}?

Possible Answers:

\displaystyle B=\begin{Bmatrix} x\ \epsilon\ S: x\leq0 \end{Bmatrix}

\displaystyle B=\begin{Bmatrix} x\ \epsilon\ S: x< 0 \end{Bmatrix}

\displaystyle B=\begin{Bmatrix} x\ \epsilon\ S: x>0 \end{Bmatrix}

\displaystyle B=\begin{Bmatrix} x\ \epsilon\ S: x\geq0 \end{Bmatrix}

None of the answers

Correct answer:

\displaystyle B=\begin{Bmatrix} x\ \epsilon\ S: x\leq0 \end{Bmatrix}

Explanation:

First, identify what is given.

\displaystyle S:\begin{Bmatrix} -6,-4,-2,0,2,4 \end{Bmatrix}

\displaystyle B=\begin{Bmatrix} -6,-4,-2,0 \end{Bmatrix}

and \displaystyle B can be described in the following format

\displaystyle B=\begin{Bmatrix} x\ \epsilon\ S: p(x) \end{Bmatrix}

Since \displaystyle B contains the elements in \displaystyle S that are less than or zero, \displaystyle p(x) can be written as follows.

\displaystyle B=\begin{Bmatrix} x\ \epsilon\ S: x\leq0 \end{Bmatrix}

Example Question #1 : Logic

\displaystyle B\subseteq \begin{Bmatrix} {3,4,7,9,11} \end{Bmatrix} over the domain \displaystyle S=P(\begin{Bmatrix} {4,7,10,12} \end{Bmatrix})

For all \displaystyle B\ \epsilon\ S which \displaystyle P(B) is true? 

Possible Answers:

\displaystyle B\ \epsilon\ \begin{Bmatrix} 4,7 \end{Bmatrix}

\displaystyle B\ \epsilon\ \begin{Bmatrix} 3,7,10 \end{Bmatrix}

\displaystyle B\ \epsilon\ \begin{Bmatrix} 4,7,11 \end{Bmatrix}

\displaystyle B\ \epsilon\ \begin{Bmatrix} \O, 4,7 \end{Bmatrix}

\displaystyle B\ \epsilon\ \begin{Bmatrix} 4,12 \end{Bmatrix}

Correct answer:

\displaystyle B\ \epsilon\ \begin{Bmatrix} \O, 4,7 \end{Bmatrix}

Explanation:

This question is giving a subset \displaystyle B who lives in the domain \displaystyle S and it is asking for the partition or group of elements that live in both \displaystyle B and \displaystyle S.

Looking at what is given,

\displaystyle B\subseteq \begin{Bmatrix} {3,4,7,9,11} \end{Bmatrix}

\displaystyle S=P(\begin{Bmatrix} {4,7,10,12} \end{Bmatrix})

it is seen that both four and seven live in \displaystyle B and \displaystyle S therefore both these elements will be in the partition of \displaystyle B. Another element that also exists in both sets is the empty set.

Thus the final solution is,

\displaystyle B\ \epsilon\ \begin{Bmatrix} \O, 4,7 \end{Bmatrix}

Example Question #2 : Theory Of Positive Integers

Negate the following statement.

\displaystyle P: 17 is a prime number.

Possible Answers:

\displaystyle \sim P:17 is a prime number

\displaystyle P:17 is not a prime number

\displaystyle \sim P:17 is an odd number

\displaystyle \sim P:17 is an even number

\displaystyle \sim P:17 is not a prime number

Correct answer:

\displaystyle \sim P:17 is not a prime number

Explanation:

Negating a statement means to take the opposite of it.

To negate a statement completely, each component of the statement needs to be negated.

The given statement,

\displaystyle P: 17 is a prime number.

contains to components.

Component one: \displaystyle P:17

Component two: "is a prime number"

To negate component one, simply take the compliment of it. In mathematical terms this looks as follows,

\displaystyle \sim P:17

To negate component two, simply add a "not" before the phrase "a prime number".

Now, combine these two components back together for the complete negation.

\displaystyle \sim P:17 is not a prime number.

Example Question #3 : Theory Of Positive Integers

Determine which statement is true giving the following information.

\displaystyle P: 17 is a prime number \displaystyle Q:50 is odd

Possible Answers:

\displaystyle P\wedge Q

\displaystyle \sim (P\vee Q)

\displaystyle \sim P

\displaystyle P\vee Q

None of the answers.

Correct answer:

\displaystyle P\vee Q

Explanation:

To determine which statement is true first state what is known.

The first component of this statement is:

\displaystyle P: 17 is a prime number

This is a true statement since only one and seventeen are factors of seventeen.

The second component of this statement is:

\displaystyle Q:50 is odd

This statement is false since \displaystyle 50 \mod 2=0.

Therefore, the only true statement is the one that uses the "or" operator because only one component is true.

Thus the correct answer is,

\displaystyle P\vee Q

Example Question #3 : Theory Of Positive Integers

\displaystyle B\subseteq \begin{Bmatrix} {2,10,11,23} \end{Bmatrix} over the domain \displaystyle S=P(\begin{Bmatrix} {10,20,30} \end{Bmatrix})

For all \displaystyle B\ \epsilon\ S which \displaystyle P(B) is true? 

Possible Answers:

\displaystyle B\ \epsilon\ \begin{Bmatrix} 10 \end{Bmatrix}

\displaystyle B\ \epsilon\ \begin{Bmatrix} \O, 10,20 \end{Bmatrix}

\displaystyle B\ \epsilon\ \begin{Bmatrix} \O, 10 \end{Bmatrix}

\displaystyle B\ \epsilon\ \begin{Bmatrix} 10,23 \end{Bmatrix}

\displaystyle B\ \epsilon\ \begin{Bmatrix} \O \end{Bmatrix}

Correct answer:

\displaystyle B\ \epsilon\ \begin{Bmatrix} \O, 10 \end{Bmatrix}

Explanation:

This question is giving a subset \displaystyle B who lives in the domain \displaystyle S and it is asking for the partition or group of elements that live in both \displaystyle B and \displaystyle S.

Looking at what is given,

\displaystyle B\subseteq \begin{Bmatrix} {2,10,11,23} \end{Bmatrix}

\displaystyle S=P(\begin{Bmatrix} {10,20,30} \end{Bmatrix})

it is seen that only ten lives in \displaystyle B and \displaystyle S therefore both these elements will be in the partition of \displaystyle B. Another element that also exists in both sets is the empty set.

Thus the final solution is,

\displaystyle B\ \epsilon\ \begin{Bmatrix} \O, 10 \end{Bmatrix}

Example Question #1 : Theory Of Positive Integers

Which of the following is a property of a relation?

Possible Answers:

Symmetric Property

All are properties of a relation

Partition Property

Non-symmetric Property

Equivalency Property

Correct answer:

Symmetric Property

Explanation:

For a relation to exist there must be a non empty set present. If a non empty set is present then there are three relation properties.

These properties are:

I. Reflexive Property

\displaystyle x\approx x

II. Symmetric Property

\displaystyle x\approx y\rightarrow y\approx x

III. Transitive Property

\displaystyle x\approx y, y\approx z \rightarrow x\approx z

When all three properties represent a specific set, then that set is known to have an equivalence relation.

Example Question #5 : Theory Of Positive Integers

What is an equivalency class?

Possible Answers:

\displaystyle [x]=\begin{Bmatrix} y\ \epsilon\ A, -x\approx y \end{Bmatrix}

\displaystyle [x]=\begin{Bmatrix} y\ \epsilon\ A, x\approx y \end{Bmatrix}

\displaystyle [x]=\begin{Bmatrix} y\ \epsilon\ A, x>y \end{Bmatrix}

\displaystyle [x]=\begin{Bmatrix} y\ \epsilon\ A\end{Bmatrix}

\displaystyle [x]=\begin{Bmatrix} x\approx y \end{Bmatrix}

Correct answer:

\displaystyle [x]=\begin{Bmatrix} y\ \epsilon\ A, x\approx y \end{Bmatrix}

Explanation:

An equivalency class is a definitional term.

Suppose \displaystyle A is a non empty set and \displaystyle \approx is an equivalency relation on \displaystyle A. Then \displaystyle x belonging to \displaystyle A is a set that holds all the elements that live in \displaystyle A that are equivalent to \displaystyle x.

In mathematical terms this looks as follows,

\displaystyle [x]=\begin{Bmatrix} y\ \epsilon\ A, x\approx y \end{Bmatrix}

Example Question #2 : Theory Of Positive Integers

Which of the following is a property of a relation?

Possible Answers:

All are relation properties

Equivalency Property

Non-symmetric Property

Associative Property

Reflexive Property

Correct answer:

Reflexive Property

Explanation:

For a relation to exist there must be a non empty set present. If a non empty set is present then there are three relation properties.

These properties are:

I. Reflexive Property

\displaystyle x\approx x

II. Symmetric Property

\displaystyle x\approx y\rightarrow y\approx x

III. Transitive Property

\displaystyle x\approx y, y\approx z \rightarrow x\approx z

When all three properties represent a specific set, then that set is known to have an equivalence relation.

Example Question #3 : Theory Of Positive Integers

Which of the following is a property of a relation?

Possible Answers:

Partition Property

All are properties of relations.

Transitive Property

Non-symmetric Property

Equivalency Property

Correct answer:

Transitive Property

Explanation:

For a relation to exist there must be a non empty set present. If a non empty set is present then there are three relation properties.

These properties are:

I. Reflexive Property

\displaystyle x\approx x

II. Symmetric Property

\displaystyle x\approx y\rightarrow y\approx x

III. Transitive Property

\displaystyle x\approx y, y\approx z \rightarrow x\approx z

When all three properties represent a specific set, then that set is known to have an equivalence relation.

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