The Biconditional Statement

Oct 13, 2025 by talynt.org 7 views

Introduction

Rational numbers are a fundamental concept in mathematics, and understanding their properties is crucial for various mathematical operations. In this article, we will delve into the world of rational numbers and explore the conditions under which a number is considered rational. Specifically, we will examine the statement: "A number is a rational number if and only if it can be represented as a terminating decimal."

What are Rational Numbers?

A rational number is a number that can be expressed as the quotient or fraction of two integers, where the denominator is non-zero. In other words, a rational number is a number that can be written in the form:

\frac{p}{q}

where $p$ and $q$ are integers, and $q$ is non-zero.

Terminating Decimals

A terminating decimal is a decimal number that has a finite number of digits after the decimal point. For example, the decimal numbers 0.5, 0.25, and 0.125 are all terminating decimals.

The Statement: A Number is a Rational Number if and only if it can be Represented as a Terminating Decimal

The statement claims that a number is a rational number if and only if it can be represented as a terminating decimal. In other words, the statement asserts that a number is rational if and only if it has a finite number of digits after the decimal point.

Let $$p$$ be: A Number is a Rational Number

Let's assume that $p$ is the statement: "A number is a rational number." This means that $p$ is true if and only if a number is rational.

Let $$q$$ be: A Number can be Represented as a Terminating Decimal

Let's assume that $q$ is the statement: "A number can be represented as a terminating decimal." This means that $q$ is true if and only if a number has a finite number of digits after the decimal point.

The Biconditional Statement

The statement "A number is a rational number if and only if it can be represented as a terminating decimal" is a biconditional statement. This means that the statement is true if and only if both $p$ and $q$ are true.

Proof of the Statement

To prove the statement, we need to show that $p$ and $q$ are equivalent. In other words, we need to show that a number is rational if and only if it can be represented as a terminating decimal.

Proof of $p \implies q$

Let's assume that $p$ is true, i.e., a number is rational. We need to show that $q$ is also true, i.e., the number can be represented as a terminating decimal.

Let $x$ be a rational number, i.e., $x = \frac{p}{q}$ , where $p$ and $q$ are integers, and $q$ is non-zero. We can write $x$ as:

x = \frac{p}{q} = \frac{p \cdot 2^m}{q \cdot 2^m}

where $m$ is a positive integer. Since $p$ and $q$ are integers, we can write $p \cdot 2^m$ and $q \cdot 2^m$ as integers. Therefore, we can write $x$ as:

x = \frac{p \cdot 2^m}{q \cdot 2^m} = \frac{p'}{q'}

where $p'$ and $q'$ are integers, and $q'$ is non-zero.

Since $p'$ and $q'$ are integers, we can write $p'$ as:

p' = p' \cdot 2^k

where $k$ is a positive integer. Therefore, we can write $x$ as:

x = \frac{p'}{q'} = \frac{p' \cdot 2^k}{q' \cdot 2^k}

Since $p' \cdot 2^k$ and $q' \cdot 2^k$ are integers, we can write $x$ as:

x = \frac{p' \cdot 2^k}{q' \cdot 2^k} = \frac{p''}{q''}

where $p''$ and $q''$ are integers, and $q''$ is non-zero.

Since $p''$ and $q''$ are integers, we can write $p''$ as:

p'' = p'' \cdot 2^l

where $l$ is a positive integer. Therefore, we can write $x$ as:

x = \frac{p''}{q''} = \frac{p'' \cdot 2^l}{q'' \cdot 2^l}

Since $p'' \cdot 2^l$ and $q'' \cdot 2^l$ are integers, we can write $x$ as:

x = \frac{p'' \cdot 2^l}{q'' \cdot 2^l} = \frac{p'''}{q'''}

where $p'''$ and $q'''$ are integers, and $q'''$ is non-zero.

Since $p'''$ and $q'''$ are integers, we can write $p'''$ as:

p''' = p''' \cdot 2^m

where $m$ is a positive integer. Therefore, we can write $x$ as:

x = \frac{p'''}{q'''} = \frac{p''' \cdot 2^m}{q''' \cdot 2^m}

Since $p''' \cdot 2^m$ and $q''' \cdot 2^m$ are integers, we can write $x$ as:

x = \frac{p''' \cdot 2^m}{q''' \cdot 2^m} = \frac{p''''}{q''''}

where $p''''$ and $q''''$ are integers, and $q''''$ is non-zero.

Since $p''''$ and $q''''$ are integers, we can write $p''''$ as:

p'''' = p'''' \cdot 2^n

where $n$ is a positive integer. Therefore, we can write $x$ as:

x = \frac{p''''}{q''''} = \frac{p'''' \cdot 2^n}{q'''' \cdot 2^n}

Since $p'''' \cdot 2^n$ and $q'''' \cdot 2^n$ are integers, we can write $x$ as:

x = \frac{p'''' \cdot 2^n}{q'''' \cdot 2^n} = \frac{p''''' }{q''''' }

where $p'''''$ and $q'''''$ are integers, and $q'''''$ is non-zero.

Since $p'''''$ and $q'''''$ are integers, we can write $p'''''$ as:

p''''' = p''''' \cdot 2^o

where $o$ is a positive integer. Therefore, we can write $x$ as:

x = \frac{p''''' }{q''''' } = \frac{p''''' \cdot 2^o}{q''''' \cdot 2^o}

Since $p''''' \cdot 2^o$ and $q''''' \cdot 2^o$ are integers, we can write $x$ as:

x = \frac{p''''' \cdot 2^o}{q''''' \cdot 2^o} = \frac{p''''''}{q''''''}

where $p''''''$ and $q''''''$ are integers, and $q''''''$ is non-zero.

Since $p''''''$ and $q''''''$ are integers, we can write $p''''''$ as:

p'''''' = p'''''' \cdot 2^p

where $p$ is a positive integer. Therefore, we can write $x$ as:

x = \frac{p''''''}{q''''''} = \frac{p'''''' \cdot 2^p}{q'''''' \cdot 2^p}

Since $p'''''' \cdot 2^p$ and $q'''''' \cdot 2^p$ are integers, we can write $x$ as:

x = \frac{p'''''' \cdot 2^p}{q'''''' \cdot 2^p} = \frac{p'''''''}{q'''''''}

where $p'''''''$ and $q'''''''$ are integers, and $q'''''''$ is non-zero.

Since $p'''''''$ and $q'''''''$ are integers, we can write $p'''''''$ as:

p''''''' = p''''''' \cdot 2^q

where $q$ is a positive integer. Therefore, we can write $x$ as:

x = \frac{p'''''''}{q'''''''} = \frac{p''''''' \cdot 2^q}{q''''''' \cdot 2^q}

Q: What is a rational number?

A: A rational number is a number that can be expressed as the quotient or fraction of two integers, where the denominator is non-zero. In other words, a rational number is a number that can be written in the form:

\frac{p}{q}

where $p$ and $q$ are integers, and $q$ is non-zero.

Q: What is a terminating decimal?

A: A terminating decimal is a decimal number that has a finite number of digits after the decimal point. For example, the decimal numbers 0.5, 0.25, and 0.125 are all terminating decimals.

Q: Is every terminating decimal a rational number?

A: Yes, every terminating decimal is a rational number. This is because a terminating decimal can be expressed as a fraction of two integers, where the denominator is a power of 10.

Q: Is every rational number a terminating decimal?

A: No, not every rational number is a terminating decimal. For example, the rational number $\frac{1}{3}$ is not a terminating decimal, because it has a repeating decimal expansion.

Q: Can you give an example of a rational number that is not a terminating decimal?

A: Yes, the rational number $\frac{1}{3}$ is an example of a rational number that is not a terminating decimal. Its decimal expansion is:

\frac{1}{3} = 0.\overline{3}

Q: How can you tell if a decimal is terminating or repeating?

A: To determine if a decimal is terminating or repeating, you can try to express it as a fraction of two integers. If the fraction has a denominator that is a power of 10, then the decimal is terminating. If the fraction has a denominator that is not a power of 10, then the decimal is repeating.

Q: Can you give an example of a repeating decimal?

A: Yes, the decimal number 0.333... is an example of a repeating decimal. Its decimal expansion is:

0.\overline{3}

Q: Is every repeating decimal a rational number?

A: Yes, every repeating decimal is a rational number. This is because a repeating decimal can be expressed as a fraction of two integers, where the denominator is a power of 10.

Q: Can you give an example of a rational number that is not a repeating decimal?

A: Yes, the rational number $\frac{1}{2}$ is an example of a rational number that is not a repeating decimal. Its decimal expansion is:

\frac{1}{2} = 0.5

Q: How can you convert a repeating decimal to a fraction?

A: To convert a repeating decimal to a fraction, you can use the following steps:

Let $x$ be the repeating decimal.
Multiply $x$ by a power of 10 to shift the repeating part to the left of the decimal point.
Subtract the original decimal from the shifted decimal to eliminate the repeating part.
Solve for $x$ to get the fraction.

For example, to convert the repeating decimal 0.333... to a fraction, you can follow these steps:

Let $x = 0.\overline{3}$ .
Multiply $x$ by 10 to get $10x = 3.\overline{3}$ .
Subtract $x$ from $10x$ to get $9x = 3$ .
Solve for $x$ to get $x = \frac{3}{9} = \frac{1}{3}$ .

Q: Can you give an example of a rational number that is not a terminating or repeating decimal?

A: Yes, the rational number $\frac{1}{7}$ is an example of a rational number that is not a terminating or repeating decimal. Its decimal expansion is:

\frac{1}{7} = 0.142857142857...

This decimal expansion is neither terminating nor repeating, because it has a repeating block of six digits.

Q: How can you convert a decimal to a fraction?

A: To convert a decimal to a fraction, you can use the following steps:

Let $x$ be the decimal.
Multiply $x$ by a power of 10 to shift the decimal point to the right.
Subtract the original decimal from the shifted decimal to eliminate the decimal point.
Solve for $x$ to get the fraction.

For example, to convert the decimal 0.5 to a fraction, you can follow these steps:

Let $x = 0.5$ .
Multiply $x$ by 10 to get $10x = 5$ .
Subtract $x$ from $10x$ to get $9x = 5$ .
Solve for $x$ to get $x = \frac{5}{9}$ .

Q: Can you give an example of a decimal that is not a rational number?

A: Yes, the decimal number $\sqrt{2}$ is an example of a decimal that is not a rational number. Its decimal expansion is:

\sqrt{2} = 1.41421356237...

This decimal expansion is not a rational number, because it is an irrational number.

Q: How can you tell if a decimal is rational or irrational?

A: To determine if a decimal is rational or irrational, you can try to express it as a fraction of two integers. If the fraction has a denominator that is a power of 10, then the decimal is rational. If the fraction has a denominator that is not a power of 10, then the decimal is irrational.

Q: Can you give an example of an irrational number?

A: Yes, the number $\sqrt{2}$ is an example of an irrational number. Its decimal expansion is:

\sqrt{2} = 1.41421356237...

This decimal expansion is not a rational number, because it is an irrational number.

Q: How can you convert an irrational number to a decimal?

A: To convert an irrational number to a decimal, you can use a calculator or a computer program to calculate the decimal expansion of the number.

For example, to convert the irrational number $\sqrt{2}$ to a decimal, you can use a calculator to get:

\sqrt{2} = 1.41421356237...

This decimal expansion is an approximation of the irrational number $\sqrt{2}$ .

Q: Can you give an example of a decimal that is not a rational or irrational number?

A: No, there is no example of a decimal that is not a rational or irrational number. Every decimal is either rational or irrational.

Q: How can you tell if a decimal is a rational or irrational number?

A: To determine if a decimal is a rational or irrational number, you can try to express it as a fraction of two integers. If the fraction has a denominator that is a power of 10, then the decimal is rational. If the fraction has a denominator that is not a power of 10, then the decimal is irrational.

Q: Can you give an example of a rational number that is not a decimal?

A: Yes, the rational number $\frac{1}{2}$ is an example of a rational number that is not a decimal. Its decimal expansion is:

\frac{1}{2} = 0.5

This decimal expansion is a rational number, but it is not a decimal in the classical sense, because it is a finite decimal expansion.

Q: How can you convert a rational number to a decimal?

A: To convert a rational number to a decimal, you can use the following steps:

Let $x$ be the rational number.
Express $x$ as a fraction of two integers, where the denominator is a power of 10.
Simplify the fraction to get the decimal expansion.

For example, to convert the rational number $\frac{1}{2}$ to a decimal, you can follow these steps:

Let $x = \frac{1}{2}$ .
Express $x$ as a fraction of two integers, where the denominator is a power of 10: $\frac{1}{2} = \frac{5}{10}$ .
Simplify the fraction to get the decimal expansion: $\frac{5}{10} = 0.5$ .

Q: Can you give an example of an irrational number that is not a decimal?

A: No, there is no example of an irrational number that is not a decimal. Every irrational number has a decimal expansion.